OPINION

AGEE, Circuit Judge:

Timothy Tyrone Horton appeals his conviction for possessing a firearm while a convicted felon, in violation of 18 U.S.C. §§ 922(g)(1) and 924, and also appeals the district court's imposition of a sentence of life imprisonment. For the reasons set forth herein, we affirm Horton's conviction. We conclude, however, that the district court erred in applying the murder cross-reference provision in United States Sentencing Guidelines Manual ("USSG" or "Guidelines") § 2K2.1(c)(1) and in treating as relevant conduct a murder that occurred during the course of an unrelated and uncharged offense, which error substantially increased Horton's advisory Guidelines range. Accordingly, we vacate Horton's sentence and remand for resentencing.

I. Background and Proceedings Below

The offense for which Horton was charged, and ultimately convicted by a jury, occurred on August 10, 2007.1 On that date, Horton was at the home of his girlfriend, Timeca Bryant. The couple argued after Ms. Bryant learned Horton had a gun, which he told her he was holding for a friend. Horton left the home and, while outside, fired three shots, one of which hit Ms. Bryant's unoccupied vehicle. He fired the other two into the air. Ms. Bryant came out and obtained Horton's gun. She then returned to her home, taking the gun with her, and locked herself inside. Once inside, she called the police, and Horton left the premises. When police arrived, officers found three spent .22 casings, a bullet hole in Ms. Bryant's car, and retrieved from Ms. Bryant the gun — a .22 rifle with a sawed-off stock and sawed-off barrel. Investigation revealed that the gun had been stolen during a breaking and entering of an Exxon store in July 2006.

In February 2008, Horton contacted the police and said he wanted to speak with them about this incident, at which point he confessed to possession of the gun on August 10, 2007. He was arrested and charged in this case with violating 18 U.S.C. §§ 922(g)(1) and 924, being a felon in possession of a firearm.

Horton pled not guilty and proceeded to a trial by jury. The jury in his first trial was unable to reach a verdict and the court declared a mistrial. After a second trial, the jury found Horton guilty and he was sentenced by the district court to life imprisonment. Horton filed a timely motion for new trial, which the district court denied. He timely appealed from both the conviction and sentence, and from the denial of his motion for new trial.

This Court has jurisdiction pursuant to 28 U.S.C. § 1291 and 18 U.S.C. § 3742.

II. Challenges to the Conviction

Horton raises two challenges to his conviction. First, he contends that the district court abused its discretion in denying his motion for substitution of counsel. Second, he argues that the district court abused its discretion in denying his motion for new trial predicated on what Horton describes as the Government's failure to disclose material impeachment evidence under Brady v. Maryland, 373 U.S. 83, 83 S.Ct. 1194, 10 L.Ed.2d 215 (1963). For the reasons discussed below, we reject both of these challenges.

A. Motion to Substitute Counsel

We first address Horton's claim that the district court erred in denying his motion for substitute counsel. Clarke Speaks was appointed as Horton's counsel on March 25, 2008. On October 1, 2008, two months before his scheduled arraignment, Horton filed a pro se motion for substitute counsel, his first such motion. In the motion, Horton asserted that he was "not satisfied with Mr. Clark Speaks [sic] representation and believe[d] it [to] be in [his] best [i]nterest for a change of counsel...." (JA 87.) He offered no additional details in support of his motion.

The district court denied the motion without a hearing in an order filed October 7, 2008. In that order, the court "advised" Horton that, although "he has a Constitutional right to court-appointed counsel if he is unable to afford an attorney, he is not entitled to appointment of the attorney of his choice." (JA 88 (citations omitted).) The order further informed Horton that he could "go forward with his court-appointed counsel, Mr. Speaks," or he could "represent himself, with Mr. Speaks acting as back-up counsel to assist him with legal questions that may arise." (Id. at 89.) In its order, the district court also noted that Horton would be required prior to his arraignment on December 8, 2008, to advise the court under oath whether he wanted to continue with Speaks' representation or to represent himself with Speaks as back-up counsel. This inquiry never took place, although the court did ask general questions regarding Horton's satisfaction with this attorney, and Horton did not express any dissatisfaction. Neither Horton nor Speaks ever raised the issue with the court again and Speaks represented Horton at both trials.

On February 17, 2010, approximately three months after the jury verdict convicting Horton, Speaks moved to withdraw from representation. His motion included the statement that he and Horton, "[d]uring the course of the Attorney-Client Relationship... have reached an impasse resulting from irreconcilable differences" and that this impasse was "prevent[ing] the communication necessary to prepare and implement an adequate defense." (JA 587.) The court granted the motion without a hearing, and directed the Federal Public Defender to assign substitute counsel, which was done.

We review the denial of Horton's motion for substitute counsel for abuse of discretion. See United States v. Smith, 640 F.3d 580, 587-91 & n. 6 (4th Cir.2011). In cases where a district court has denied a request by a defendant to replace one court-appointed lawyer with another court-appointed lawyer, this Court considers three factors to determine whether the initial appointment "ceased to constitute Sixth Amendment assistance of counsel": "(1) the timeliness of the motion; (2) the adequacy of the court's subsequent inquiry; and (3) `whether the attorney/client conflict was so great that it had resulted in total lack of communication preventing an adequate defense.'" Id. at 588 (quoting United States v. Gallop, 838 F.2d 105, 108 (4th Cir.1988)).

Applying these factors here, it is clear that the motion was timely made, and the Government does not contend otherwise. Similarly, the Government does not contend-nor could it-that the district court made any inquiry into the reasons for Horton's dissatisfaction with his counsel. This fact distinguishes this case from Smith, in which there was at least some inquiry into the reasons for the dissatisfaction and we held there was no abuse of discretion. Here, because of the district court's complete failure to conduct any inquiry, this Court is essentially left with an incomplete record upon which to determine the third factor: the extent of the breakdown in communication and whether it was so great that it prevented an adequate defense. Accordingly, we will assume, without deciding, that the district court abused its discretion in denying Horton's motion without conducting any inquiry into the reasons for his dissatisfaction with counsel or any inquiry as to the extent of any breakdown in communication.

We nonetheless conclude that Horton is not entitled to a reversal of his conviction because the error was harmless and did not result in any prejudice to him. See, e.g., Fed.R.Crim.P. 52(a) ("Any error, defect, irregularity, or variance that does not affect substantial rights must be disregarded."); United States v. Young, 470 U.S. 1, 13 n. 10, 105 S.Ct. 1038, 84 L.Ed.2d 1 (1985) (in addressing claim of prosecutorial misstatements, "a reviewing court could reverse an otherwise proper conviction only after concluding that the error was not harmless."); United States v. Wilks, 46 F.3d 640, 644 (7th Cir.1995) ("Even if ... the district court abused its discretion when it denied [the defendant's] request for new counsel, such an error [was] harmless" because defendant failed to show that counsel rendered constitutionally ineffective assistance and thus there was no Sixth Amendment violation).

In this case, there is clear evidence that Speaks provided an adequate defense at both trials. For example, he filed pre-trial motions in limine, he cross-examined government witnesses, and he strongly advocated for his client throughout both trial proceedings. Indeed, the first trial resulted in a hung jury, which is attributable in some part to Speaks' performance as an adequate advocate for Horton.

Notably, Horton does not identify — let alone show — any specific way in which his defense was hampered by any lack of communication with his counsel. In fact, on two different occasions after Horton's motion to substitute was denied, he appeared before the district court and was placed under oath. By his failure to assert otherwise in response to questions posed by the court, Horton indicated that he had "ample opportunity to discuss his case with his attorney," that he had "discussed his case with his attorney," and that he was "completely and fully satisfied with his attorney's services." (JA 103, JA 120.) Thus, Horton's own representations to the court refute that there were significant communication problems prior to or during the trials.2

The record indicates that at some point after Horton was convicted and prior to sentencing, when counsel asked to withdraw and was in fact replaced, communication had broken down to some extent between Speaks and Horton. But based on the complete record before us, we conclude that any error in failing to appoint substitute counsel at the time Horton requested it was harmless. Accordingly, Horton is not entitled to have his conviction vacated on this ground.

B. Motion for New Trial

Horton's second challenge to his conviction is based on the district court's denial of his motion for a new trial. In that motion, he alleged that the Government failed to disclose material impeachment evidence until after his trials. He argues on appeal that the district court's order denying his motion constituted an abuse of discretion and that he is entitled to a new trial.

Horton's argument as to the alleged Brady evidence focuses on the testimony of two police officers regarding his confession to the charged offense, which was not videotaped, and the reasons for the failure to do so. Specifically, at both trials the juries heard evidence concerning Horton's unrecorded confession to possessing the firearm, which he made during a custodial interview on February 4, 2008. There were two officers present at the time of Horton's confession, ATF Special Agent Fanelly and Raleigh Police Department Officer Nickel.3 Fanelly was conducting the interview and Nickel was merely present. At Horton's first trial, Fanelly testified that he did not record the interview because ATF agents never record interviews, he did not know if the interview room was equipped with recording devices, and he did not know how to use such devices. Nickel did not testify at the first trial.

At the second trial, both officers testified that the reason they did not record their interrogation of Horton was that it did not relate to a homicide investigation, and the law only required such recording as part of homicide investigations.4 Fanelly also testified that, at the start of the interview, he "told [Horton] what [they were] there to talk about, and [Horton] said he wanted to talk about the — his arrest for having the gun at — recovered at his girlfriend's house." (JA 446.)

On appeal, Horton attaches much significance to the fact that both juries asked questions regarding his confession. In the first trial, the jury inquired whether Horton's statement to the police was documented. In the second, the jury asked to "see [a] transcript of the interview ... if there is one[.]" (JA 521.) Horton posits that the additional explanation offered by the officers at his second trial, which he contends was false, tipped the scales in favor of conviction.

In his motion for new trial, Horton claimed that an investigative police report prepared by R. Miller of the Raleigh Police Department ("the Miller Report") was Brady evidence that should have been disclosed prior to trial, but which was not. According to Horton, the report shows that, by at least October 9, 2007, the "Raleigh Police Department was, in fact, conducting a homicide investigation of Horton" and that "Fanelly was, in fact, involved in [that] investigation." (JA 821, Mot. for New Trial.) Horton argued that he was entitled to a new trial because the Government never disclosed that report to him,5 and he "should [have been] able to use [the Miller Report] to rebut Nickel's and Fanelly's testimonies that they declined to record their 4 February 2008 interview of Horton on the ground that said interview was not related to a homicide investigation, as well as to impeach Nickel's and Fanelly's credibility for testifying to same." (JA 822.)

Horton contends that, in denying his motion for new trial, the district court applied the wrong legal standard and thus abused its discretion.6 He also argues that, applying the proper standard for Brady violations, he is entitled to a new trial.

In response, the Government posits that, although the report itself might not have been disclosed prior to trial, both "the defendant and trial counsel were aware, well before the first trial, that the defendant was [the] subject of an ongoing homicide investigation at the time he was interviewed on February 4, 2008. (See J.A. 46, 60, 67-69, 72, 82-83.)" (Gov't Br. at 42.) As the Government notes, at the hearing on Horton's motion to suppress, Fanelly testified that he had informed Horton he was being investigated for a number of crimes, including "a drug-related homicide" (JA 67), but that Horton "said he didn't want to talk about the homicide or the carjacking, that he just wanted to talk about the gun recovery from August 10th." (JA 69.) Fanelly further testified at the suppression hearing that he made it "perfectly clear" to Horton that he (Fanelly) wanted to talk about the homicide, but when Horton refused to discuss it, Fanelly let him talk about the August 10, 2007 incident. (JA 72.) So, the fact that Horton was a homicide suspect at the time of the February 2008 interview was well known to Horton and his counsel at least as early as the suppression hearing, and certainly before trial.

The Government further points to the important fact that Horton's "trial counsel successfully moved in limine before both trials to exclude from evidence `any reference to the existence [of other pending charges], as well as any detail or circumstances surrounding such charges.'" (Gov't Br. at 44 (alteration in original).) Accordingly, to introduce evidence of the Miller Report or the mere fact that Horton was a homicide suspect would have contradicted the district court's prior ruling on Horton's own motion in limine. Finally, the Government argues that Horton is overstating on appeal the impeachment value of the Miller Report. The Government's arguments are convincing.

The standard of review here is settled:

United States v. Wilson, 624 F.3d 640, 660-61 n. 24 (4th Cir.2010). As we have noted, the district court applied the wrong legal standard to Horton's claim, see supra at note 6, but the record before us is fully developed such that we can address Horton's argument as to an alleged Brady violation de novo. Applying the proper legal standard, we conclude that Horton has not established that a Brady violation occurred or that he is entitled to a new trial.

In Wilson, we set forth the basic framework of analysis for a new trial motion based on a Brady violation:

624 F.3d at 660-61.

We further explained the relevant concepts as follows: "Evidence is `exculpatory' and `favorable' if it `may make the difference between conviction and acquittal' had it been `disclosed and used effectively.' United States v. Bagley, 473 U.S. 667, 676, 105 S.Ct. 3375, 87 L.Ed.2d 481 (1985). Evidence is `material' if it is `likely to have changed the verdict.' Moseley v. Branker, 550 F.3d 312, 318 (4th Cir.2008)." Wilson, 624 F.3d at 661; see Winston v. Kelly, 592 F.3d 535, 556 (4th Cir.2010) ("[T]he materiality element of a Brady claim requires a collective assessment of whether introduction of the exculpatory evidence might have affected the outcome of the trial.").

Applying this test here, we conclude that Horton cannot satisfy the second factor, i.e., that introduction of the exculpatory evidence might have affected the outcome of the trial; we thus need not address the first or third factors.7 Importantly, we agree with the Government that the Miller Report would have had a minimal impact, if any, on the credibility of the officers. This is so because the officers had a plausible explanation, consistent with their testimony and the Miller Report, that renders the report largely insignificant. That is, Fanelly testified at the suppression hearing that Horton was a suspect in a homicide, but that the interview itself did not relate to the homicide, because Horton repeatedly told the officers he did not want to talk about the homicide. There is nothing in Fanelly's explanation that is inconsistent with the Miller Report's conclusion that Horton was brought in as a homicide suspect, but then (from the start of the interview, when Horton refused to be interviewed about anything other than the gun possession incident on August 10, 2007), that interview was not related to the homicide investigation.

Indeed, Horton's own motion in limine was at least one factor that prevented Fanelly from providing a fuller explanation to the jury.8 Because Fanelly was not permitted to state that Horton was being investigated for a homicide, he could not explain before the jury that the interview did not relate to a homicide because Horton refused to discuss it and instead would only talk about the gun possession charge on August 10, 2007. Fanelly was able to explain that fact fully at the suppression hearing (when the jury was not present), and gave as full an explanation as he could to the jury at the second trial, without violating Horton's in limine motion. At argument before this Court, Horton's counsel admitted that, if the Miller Report had been available to trial counsel and he had used it for impeachment purposes, the jury would have learned that Horton was a suspect in a homicide, evidence that Horton obviously believed was prejudicial, or he would not have moved in limine to exclude it. Given this trade-off, we think it highly unlikely that, if counsel elected to use it as impeachment evidence, this evidence would have changed the outcome of Horton's trial. It borders on the disingenuous for Horton to claim the benefits of the granted motion in limine at trial, but now seek to eschew it on appeal.

Moreover, there was strong evidence against Horton other than his confession, including the testimony of his girlfriend at the time of the incident. The Government also introduced into evidence the spent shell casings and the gun itself that were recovered from the ground outside Ms. Bryant's home and from inside her home, respectively. Additionally, the officer who initially reported to the scene testified that he observed a bullet hole in Ms. Bryant's car, and that Ms. Bryant appeared "a little shaken and upset" when he arrived. (JA 402.) Thus, the credibility of the officers as to Horton's confession, while important to the case against him, was only part of the case presented to the jury. In short, no Brady violation occurred and Horton is not entitled to a new trial.

III. Challenges to the Sentence

Horton also appeals his sentence, challenging on appeal the district court's application of the murder cross-reference. He raises four separate claims of error (three of which relate to the application of the cross-reference), but because of our holding, we need only address two.9 The first claim we address is Horton's argument that the district court erred in its factual finding that he was present or involved in the home invasion and robbery during which the murder occurred. The second is his argument that the district court misapplied the Guidelines and erred in concluding that the murder was "relevant conduct" to the offense of conviction. We address each of these challenges in turn.

In doing so, we are mindful of our role, which is that "[w]e review a sentence for reasonableness, applying an abuse of discretion standard." United States v. Susi, 674 F.3d 278, 282 (4th Cir.2012) (citing Gall v. United States, 552 U.S. 38, 49, 128 S.Ct. 586, 169 L.Ed.2d 445 (2007)).

Id.

In this case, because we conclude that the district court committed a significant procedural error, we do not reach the substantive reasonableness of Horton's sentence. See United States v. Carter, 564 F.3d 325, 328 (4th Cir.2009) (appellate court can consider the substantive reasonableness of a sentence "[i]f, and only if" it "find[s] the sentence procedurally reasonable"); id. at 330 n. 4 ("Having found the sentence procedurally unreasonable, ... we cannot review the sentence for substantive reasonableness.").

A. Additional Background as to Sentencing

The presentence report ("PSR") prepared by the Probation Office first discussed the facts of the only offense charged in the indictment and the only offense of which Horton was convicted — the August 10, 2007 events at Ms. Bryant's home. Nonetheless, the bulk of the sentencing proceeding was devoted to testimony regarding a second incident, which the PSR determined — and the district court agreed — was "relevant conduct."

According to the PSR, this second incident occurred on August 17, 2007, one week after Horton possessed the firearm and fired the shots outside Ms. Bryant's home. On August 17, five adults and five children were present in an apartment in Raleigh when one of the adults, Charmeka Harris, opened the door in response to knocking. Three masked individuals, at least two of whom were armed, then barged into the apartment and robbed the occupants of various belongings at gunpoint. Upon entering the residence, one of the assailants shot Ms. Harris in the stomach with a sawed-off shotgun and she later died from the injury.

There were numerous inconsistencies in the victim and witness statements regarding various aspects of the home invasion, including how many assailants participated, how many of them were armed, and what they looked like, to the extent that they were not disguised. The attempts by victims to identify the assailants through subsequent line-ups were unsuccessful and the shotgun was never recovered.

In addition to the victims and some non-victim witnesses at the apartment complex, several other individuals provided statements to authorities concerning their knowledge of the robbery/murder. Most of these were from persons who indicated they had heard the alleged perpetrators of the robbery discussing it, or heard second-hand of comments made by them. Some of these statements implicated Horton, either as being involved in the robbery or being the shooter, and others indicated that he was not present or involved and instead identified others as the perpetrators. Ultimately, the police investigation into the incident identified Horton and four others whom the investigators believed were participants in the robbery.10

Based on the foregoing, the PSR concluded that

(JA 935, ¶ 5.) Accordingly, the PSR computed and explained Horton's base offense level as follows:

(JA 947, ¶ 46.)

At sentencing, the district court heard testimony from two police detectives who had investigated the home invasion and shooting concerning their investigation and the various statements they received. The court ultimately concluded that the preponderance of the evidence supported the finding that Horton possessed a firearm during the August 17, 2007 robbery/home invasion.

The district court further found the August 17 murder was relevant conduct to the August 10 instant offense, which led to the significant increase in Horton's base offense level based on the cross-referencing provision. The district court thus adopted the PSR's computation of Horton's base offense level, which used the Guideline for First Degree Murder (USSG § 2A1.1) instead of the lower offense level for a simple felon-in-possession charge. (Id. at 947, ¶ 46.) This resulted in a base offense level of 43 instead of the lower offense level applicable to § 922(g)(1) violations.11

Horton had 15 criminal history points, establishing a criminal history category of VI. He was also an armed career criminal, which provides an independent ground for establishing a criminal history category of VI. The advisory Guidelines range, as determined by the district court, called for life imprisonment, and the applicable statutory provision (18 U.S.C. § 924(e)) required a mandatory minimum of not less than 15 years. The district court imposed a sentence of life imprisonment.

B. Factual Finding as Error

In assessing whether a district court properly calculated the Guidelines range, including its application of any sentencing enhancements, this Court "review[s] the district court's legal conclusions de novo and its factual findings for clear error." United States v. Layton, 564 F.3d 330, 334 (4th Cir.2009).

We first address Horton's contention that the district court clearly erred in finding, as a factual matter and by a preponderance of the evidence, that Horton was involved in the August 17, 2007 robbery and responsible for the murder of Ms. Harris. As noted, we review this factual finding only for "clear error," which is a very deferential standard of review, allowing us to reverse only if we are "left with a definite and firm conviction that a mistake has been committed." F.C. Wheat Mar. Corp. v. United States, 663 F.3d 714, 723 (4th Cir.2011). While there was some conflicting evidence on the point, the district court heard extensive testimony from two agents regarding the investigation into the murder of Ms. Harris and there was sufficient evidence to support a finding, by a preponderance of the evidence, that Horton committed the murder. Thus, to the extent that Horton challenges the district court's factual finding that he committed the murder as unsupported by reliable evidence, he has not shown error under the applicable standard of review.12

That fact alone, however, does not establish the propriety of applying the cross-reference. As noted, Horton also argues that, even assuming the district court's factual finding that he committed the murder was proper, the application of the cross-reference is nonetheless improper. We turn to this contention next.

C. Application of the Cross-Reference

As noted above, the PSR recommended — and the district court concluded — that the August 17, 2007 robbery and murder were relevant conduct for sentencing purposes. In assessing the propriety of that determination, three provisions of the Sentencing Guidelines are pertinent: (1) USSG § 2K2.1(c)(1) ("the Cross-Reference Provision"); (2) USSG § 1B1.3 ("the Relevant Conduct Guideline"); and (3) USSG § 3D1.2 ("the Grouping Guideline"). We now discuss the interrelation of these provisions in determining whether the district court erred in its Guidelines determination.

The offense level for a violation of 18 U.S.C. § 922(g)(1), the offense of conviction here, is established under USSG § 2K2.1. Subsection (c) of this Guideline, the Cross-Reference Provision, states in relevant part:

USSG § 2K2.1(c)(1).

Applicability of the Cross-Reference Provision, in turn, depends on whether the cross-referenced offense constitutes relevant conduct under the Relevant Conduct Guideline. See USSG § 1B1.3(a) (cross-references are to be determined on the basis of relevant conduct unless otherwise specified); United States v. Pauley, 289 F.3d 254, 258 (4th Cir.2002), vacated in non-relevant part on reh'g, 304 F.3d 335 (4th Cir.2002) (per curiam), ("Under the scheme created by the [USSG], whether a particular cross-reference should be applied depends on whether the conduct to which the cross-reference refers is `relevant conduct'" as defined in the Relevant Conduct Guideline). Put differently, only conduct that also falls within the scope of the Relevant Conduct Guideline can be the subject of the Cross-Reference Provision. Accordingly, we must review the Relevant Conduct Guideline to determine whether the murder here falls within its scope.

The Relevant Conduct Guideline treats as relevant conduct, including for cross-referencing purposes, the following:

USSG § 1B1.3.

As is obvious from its text, Subsection (a)(1) of the Relevant Conduct Guideline requires a closer connection between the acts and omissions committed and the offense of conviction than does Subsection (a)(2), which encompasses a broader group of acts. United States v. Johnson, 347 F.3d 635, 640 (7th Cir.2003) ("Subsection (a)(2) allows a court to consider a broader range of conduct than does the trailing clause of (a)(1). USSG § 1B1.3, cmt. background."). As a counterbalance to this broader scope, however, Subsection (a)(2) has a threshold limitation on its applicability, i.e., it is applicable "solely with respect to offenses of a character for which [the Grouping Guideline] would require grouping of multiple counts." USSG § 1B1.3(a)(2).

Notably, the Government does not contend that the August 17, 2007 robbery and murder would fall within Subsection (a)(1) of the Relevant Conduct Guideline.13 Thus, we look here only to whether the murder falls within Subsection (a)(2) which, by its express terms, requires reference to the Grouping Guideline, USSG § 3D1.2.

The Guidelines Commentary explains the interplay and purpose of the reference to the Grouping Guideline in Subsection (a)(2) as follows:

USSG § 1B1.3, cmt. background.

For purposes of this opinion, two aspects of the Grouping Guideline are significant: (1) it requires that felon-in-possession offenses be grouped; and (2) it specifically forbids the grouping of homicide offenses and other violent offenses. See USSG § 3D1.2(d) (grouping is required for offenses covered by § 2K2.1 and excluded from grouping are "all offenses in Chapter Two, Part A (except § 2A3.5)," which includes the Guideline for murder, § 2A1.1). While the parties agree on these two principles, clear from the text of the Grouping Guideline itself, they differ on how to apply these principles in this case. There is also a circuit split as to how to properly apply the Grouping Guideline when determining cross-references for murder or other violent offenses.

The Government's explanation as to why the murder cross-reference should apply (and the rationale in the PSR adopted by the district court) can be stated as follows. First, the defendant's unlawful possession of a firearm on August 17, 2007 during the robbery and murder, is groupable with the offense of conviction because both are felon-in-possession offenses. Thus, according to the Government, the procedural trigger of groupability, necessary for Subsection (a)(2) of the Relevant Conduct Guideline to apply, is satisfied. Second, the substantive requirement in Subsection (a)(2) that the two offenses be "part of the same course of conduct or common scheme or plan" is also satisfied. Third, the murder which occurred during the August 17, 2007 relevant conduct offense, is likewise relevant conduct pursuant to Subsection (a)(3) of the Relevant Conduct Guideline, which includes "all harm that resulted from the acts ... specified in [Subsection (a)(2)]."

Not surprisingly, Horton disagrees. He argues instead that the pertinent offenses for determining groupability are the offense of conviction (the August 10 felon-in-possession charge) and the offense for which the cross-reference is being applied, which in this case is murder. Because a murder offense is specifically not subject to grouping, Horton contends that the procedural trigger for application of Subsection (a)(2) of the Relevant Conduct Guideline — i.e., groupability of the two offenses — is not satisfied. Accordingly, Subsection (a)(2) cannot be utilized to render the August 17, 2007 incident relevant conduct. And, as noted, the Government does not argue that the murder is relevant conduct under Subsection (a)(1).14

There is a circuit split in the threshold issue as to whether only the offense of conviction need be a groupable offense or whether both the offense of conviction and the relevant conduct offense (the cross-referenced offense) must be groupable offenses in order to apply Subsection (a)(2). Notably, all but one of the circuits to have squarely addressed the issue have adopted Horton's view that both must be groupable. See, e.g., United States v. Williams, 431 F.3d 767, 772-73 & n. 9 (11th Cir.2005) (concluding that where conviction was for a violation of 18 U.S.C. § 922(g), the district court erred in utilizing an assault with a different firearm as relevant conduct, because assault is excluded from being grouped, and thus "the definition of relevant conduct found in § 1B1.3(a)(2) is not available to the Government"); United States v. Settle, 414 F.3d 629, 632 n. 2 (6th Cir.2005) (attempted murder is not groupable and thus could not be relevant conduct under Subsection (a)(2) in case where charge of conviction was felon-in-possession of a firearm); United States v. Jones, 313 F.3d 1019, 1023 & n. 3 (7th Cir.2002) (although holding that the Cross-Reference Provision in § 2K2.1 was appropriately applied to a murder that was relevant conduct under Subsection (a)(1), observing the murder would not be relevant conduct under Subsection (a)(2) because "the homicide charge is specifically excluded" from the Grouping Guideline); United States v. Levario-Quiroz, 161 F.3d 903, 906 (5th Cir.1998) (in applying the Cross-Reference Provision, defendant's acts of assault with attempt to commit murder and attempted murder were not "relevant conduct" under Subsection (a)(2) because, although they were part of the same course of conduct as the offense of conviction, "they were not offenses of a character for which [USSG §] 3D1.2(d) would require grouping"). But see United States v. Kulick, 629 F.3d 165, 170-71 & n. 4 (3d Cir.2010) (concluding that only the offense of conviction need be subject to grouping).

In Jones, the Seventh Circuit addressed — and rejected — the precise analysis proposed by the Government here:

313 F.3d at 1023 n. 3.15 As noted, the other circuits cited above agree.

The Third Circuit has held to the contrary. Kulick, 629 F.3d at 170-71 & nn. 4-5 (holding pursuant to the binding prior panel decision of Jansen v. United States, 369 F.3d 237, 248 (3d Cir.2004), Subsection (a)(2) is applicable "when the offense of conviction is a groupable offense, regardless of the nature of the alleged relevant conduct"). Notably, however, the Kulick court embraced its holding with little enthusiasm, instead stating that, if it were not bound by Jansen, "an argument might be made that we should not apply [Subs]ection (a)(2) on these facts...." Id. at 170 n. 4. The Kulick court also "le[ft] for another day whether to recommend en banc consideration of whether Jansen's effect should be limited to drug offenses or to those cases in which the offense of conviction has a higher offense level than the alleged relevant conduct." Id.

Now squarely faced with the same issue as our sister circuits,16 we agree with the conclusions of the Fifth, Sixth, Seventh, and Eleventh Circuits and hold that Subsection (a)(2) of the Relevant Conduct Guideline is applicable only when both the offense of conviction and the relevant conduct offense are capable of grouping. See USSG § 1B1.1 cmt. n.1(H) (defining "offenses" to "mean[s] the offense of conviction and all relevant conduct.")

We further reject the Government's argument that the relevant conduct "offense" is the second felon in possession offense occurring on August 17. As we have held above and as applied in the context of cross-references, both the offense of conviction and the cross-referenced offense must be group-able. Contrary to the Government's contention, the relevant conduct offense here is murder, because it was the murder offense and its Guideline that was used to set Horton's offense level, and it was the murder that the district court treated as "relevant conduct." As the Eleventh Circuit cogently explained in Williams:

431 F.3d at 772 n. 9. Similarly, here it is the murder that must be groupable for Subsection (a)(2) to apply "because it is the [murder] guideline that is used to calculate the offense level," and it clearly is not. See id.; Settle, 414 F.3d at 632 n. 2; Levario-Quiroz, 161 F.3d at 906; Jones, 313 F.3d at 1023 n. 3.

The Government errs in treating the felon-in-possession offense as the relevant conduct offense in order to bring it within the Grouping Guideline because that analysis ignores how the cross-reference operates. Tellingly, the cross-reference does not affect the offense level by, for example, adding a second firearm possession to the offense characteristics. Instead, it applies the offense level for murder. Because murder is excluded from the grouping rules, Subsection (a)(2) is not available to the Government to utilize the murder as the relevant conduct.17

For the foregoing reasons, we conclude the district court erred in applying the murder cross-reference under Subsection (a)(2). We therefore vacate Horton's sentence and remand for resentencing.18

IV. Conclusion

For the reasons set forth above, we affirm Horton's conviction, vacate his sentence, and remand for resentencing consistent with this opinion.

AFFIRMED IN PART, VACATED IN PART, AND REMANDED IN PART

DAVIS, Circuit Judge, concurring in part and concurring in the judgment:

I concur in most of the majority opinion and in the judgment. I agree there are no grounds for vacating the conviction, for the reasons the majority explains. I also agree that the district court procedurally erred in cross-referencing the August 17, 2007, murder of Charmeka Harris. The district court should not have, and cannot on remand, rely on the Harris murder to increase Horton's advisory term of imprisonment under the Sentencing Guidelines. That conclusion, in my view, renders it entirely unnecessary and inappropriate to consider, as the majority does in section III-B, Horton's alternative ground for challenging his life sentence: whether "the district court clearly erred in finding, as a factual matter and by a preponderance of the evidence, that Horton was involved in the August 17, 2007 robbery and responsible for the murder of Ms. Harris." Maj. Op. at 474.

I.

The upshot of our conclusion that the Harris murder cannot be cross-referenced is this: the Sentencing Commission has determined that the courts generally should not tack on punishment for crimes such as the Harris murder to sentences for crimes such as Horton's prohibited possession of the .22 rifle. In essence the Commission is telling us that Horton should only be punished for his alleged involvement in the Harris murder if the government can (and does) prove, to a jury and beyond a reasonable doubt, that Horton committed the murder. Indeed, the State of North Carolina apparently had intended to take that usual route — that is, until the district court in this case elected, erroneously, to invoke the murder cross-reference and sentence Horton to life imprisonment. At that point, the State dismissed the state charges, apparently realizing it was off the hook; it did not have to go through the effort and uncertainty of trying to prove, to a jury and beyond a reasonable doubt, that Horton was guilty of the murder.1

Because the murder is now irrelevant to the Guidelines calculation, the majority's election to address the sufficiency of the evidence underlying the cross-reference can be explained only by the following series of dubious assumptions: (a) the government will argue on remand that the district court should disregard the Commission's instruction to require that the Harris murder be charged and proven as a separate crime (or "relevant conduct" in relation to a separate crime); (b) the district court will foreclose the parties from submitting additional evidence on whether Horton committed the murder; (c) the district court will impose an upward variance under 18 U.S.C. § 3553(a) based on a finding that Horton committed the murder; and (d) a future panel of this court will find the hypothetical variant sentence substantively reasonable.

I do not think we should so easily assume the Commission was so obviously wrong, and I am not convinced the district court would so assume. Certainly, there is no authority for the district court to refuse reopening of the evidentiary record upon the resentencing. And, in any event, nothing this panel says about the evidence before the district court in the original sentencing could possibly bind a subsequent panel examining the evidentiary record created upon the remand for resentencing. Accordingly, the proper course would be to allow the district court to determine in the first instance (and undistracted by dicta from this court) whether, in its view, reliable evidence of Horton's alleged involvement in the Harris murder would justify a substantial upward variance.

II.

The majority's election to reach out and address the evidentiary sufficiency issue also highlights a certain irony. In cases in which a criminal defendant has appealed a conviction on a particular count on both sufficiency-of-the-evidence and legal grounds, and in which there was legal error, this court regularly, and in my view erroneously, declines to decide whether the evidence was sufficient to support the conviction. See, e.g., United States v. Lawson, 677 F.3d 629, 651 n. 29 (4th Cir. 2012) (declining to address sufficiency of evidence; new trial awarded on ground of juror misconduct); United States v. Golding, 168 F.3d 700, 705 n. * (4th Cir.1999) (declining to address sufficiency of evidence; new trial awarded on ground of prosecutorial misconduct); United States v. King, 650 F.2d 534, 535 n. 2 (4th Cir. 1981) (declining to address sufficiency of evidence; new trial awarded on ground of denial of right to make closing argument in derogation of Sixth Amendment); see also United States v. Sandalis, 14 Fed. Appx. 287, 291 n. 7 (4th Cir.2001) (unpub.) (suggesting that sufficiency of evidence challenge would be "moot" if new trial were to be awarded on the basis of juror misconduct), op. after remand, 39 Fed. Appx. 798, 804-05 (4th Cir.2002) (unpub.) (affirming convictions after considering, inter alia, evidentiary sufficiency).

That course is improper. Where a defendant shows on appeal that the evidence was insufficient for the government to meet its burden of proof, we must remand for the entry of a judgment of acquittal on the count unsupported by substantial evidence (irrespective of the presence of other legal error) because subjecting the defendant to a new trial would violate the Fifth Amendment's Double Jeopardy Clause. Burks v. United States, 437 U.S. 1, 11, 98 S.Ct. 2141, 57 L.Ed.2d 1 (1978). In cases where a count of conviction is tainted by legal error, we cannot fairly (or logically, I submit), decline to decide a sufficiency challenge to that count because the disposition of the appeal — remand for a new trial or remand with instructions to enter a judgment of acquittal — turns on whether the sufficiency challenge is meritorious.

Horton's appeal of his sentence, and other such appeals, are fundamentally different than appeals of convictions such as those discussed above, because in this case the Double Jeopardy Clause does not prevent the district court from allowing the government and/or Horton to present additional evidence at Horton's re-sentencing proceeding. "[T]o the extent that the mandate of the appellate court instructs or permits reconsideration of sentencing issues on remand, the district court may consider the issue de novo, entertaining any relevant evidence on that issue that it could have heard at the first hearing." United States v. Bell, 5 F.3d 64, 67 (4th Cir. 1993) (internal quotation marks omitted); cf. United States v. Gammage, 580 F.3d 777, 779 (8th Cir.2009) (remanding for the district court "to resentence Mr. Gammage based on the record already before it"). Indeed, the dearth of specific findings by the district court at Horton's initial sentencing hearing prevents us from discerning whether additional evidence might lead the court to reconsider its conclusion that the government met its burden of proof.2

Therein lies the irony of the majority's chosen course. On the one hand, in cases such as Lawson, Golding, and King, we expressly decline to decide whether a conviction was supported by substantial evidence, even though deciding that issue might entitle a defendant to a judgment of acquittal rather than a bare remand. On the other hand, in cases like this one, where resolving the sufficiency of the evidence supporting a legally erroneous sentencing enhancement is unnecessary to the disposition of the appeal — and where a defendant might well have new grounds for attacking that evidence upon resentencing — the majority uses dicta to give the government a "thumbs up," essentially predicting that the government will meet its burden again on remand.

For these reasons, the wise course for us would be to decline to decide whether the government mustered sufficient evidence to prove by a preponderance that Horton committed the August 2007 murder. Sometimes, obiter dicta is both useful and harmless. At other times, it is both useless and harmful, and thus inappropriate. This is one of those cases.

III.

In response to this concurring opinion, the majority has inserted its footnote twelve. I confess that I am perplexed by that footnote.

It is perfectly clear that the majority has confused Horton's legal claim of evidentiary sufficiency, which is the subject matter of this concurrence, with a claim of "clear error" in the district court's factfinding, i.e., a potentially curable factfinding error under the Advisory Sentencing Guidelines.3 Horton's brief, at pages 44-50, as an alternative argument to his principal (and dispositive) argument — the legal impropriety of the murder cross-reference — unmistakably challenges the sufficiency of the evidence that he was involved in the Harris murder. See Appellant's Brief at 44, Argument Heading ("A PREPONDERANCE OF THE EVIDENCE DID NOT SUPPORT THE CROSS-REFERENCE TO FIRST DEGREE MURDER"). It is Horton, not the majority, that has presented his issues "in their logical order." Because our resolution of the dispositive legal issue of the murder cross-reference fully disposes of the sentencing claim as the case comes to us, we should stop there.

The majority's response to this simple truth, see ante n. 12 ("If we had concluded that the district court clearly erred in its factual determination regarding the August 17, 2007 murder, the more complicated issue of the murder cross-reference's applicability would not have been reached.") is absolutely baffling. When a "more complicated" issue is a legal issue crying out for resolution for the benefit of the district judges in this circuit and the lawyers appearing before them, it would have been a derogation of our responsibility to clarify the law for this panel to have attempted to duck that issue, no matter how "complicated."4 And, I unhesitatingly note, the majority opinion performs that job with exquisite cogency and clarity.

Finally, the majority's reliance on dicta from United States v. Susi, 674 F.3d 278 (4th Cir.2012), is unavailing. I do not doubt that in any case this court's mandate may expressly authorize, see, e.g., Bell, 5 F.3d at 67, or it may expressly prohibit, see, e.g., Gammage, 580 F.3d at 779, a district court's reopening of the factual record upon a remand for resentencing. It is the mandate that is the sole authority for such cabining of a district court's authority. In any event, as Susi made perfectly clear, that case was decided on the basis of harmless error, not the absence of error; thus, it has no salience here. See Susi, 674 F.3d at 283 ("We need not resolve whether the district court erred in concluding that it was barred from reconsidering the Sentencing Guidelines calculation, because even if we assume that the district court erred in this respect, that error was harmless under the facts of this case.").

* * *

In sum, we should say no more than is needed in this case.