BLACKBURNE-RIGSBY, Associate Judge:

After a bench trial, appellant Jose Medina was convicted of one count of assault.1 In this consolidated appeal of his conviction and the trial court's order denying his motion for a new trial, appellant argues three grounds for reversal or remand of his conviction: (1) there was insufficient evidence to prove beyond a reasonable doubt that he assaulted the victim; (2) the trial court erred by denying his motion for a new trial without conducting a hearing; and (3) the government failed to disclose Jencks materials created by the prosecutor and several Metropolitan Police Department employees. We conclude that there was sufficient evidence to support appellant's conviction and that the trial court did not err by denying appellant's motion for a new trial without conducting a hearing. However, we remand this case to the trial court to conduct an evidentiary hearing on the discrete issue of whether the government complied with the Jencks Act with respect to notes taken by Sergeant Mercier during his meetings with the prosecutor and the government's key witness, Officer Gallagher.

I.

In the early morning of October 14, 2006, Metropolitan Police Department (MPD) Officers Edward Shymansky and Delmar Gallagher arrested Buony Roum and brought him to the Third District Police Station for processing. At the station, appellant, an MPD detective, briefly interviewed Roum. After the interview, Officers Shymansky and Gallagher put Roum in handcuffs and brought him into the hallway, where they left him standing while they collected his personal property.

At this point, appellant walked by Roum and became involved in a verbal exchange with him, during which Roum referred to appellant with a racial slur.2 Officer Gallagher, who observed the encounter while standing several feet away, testified that appellant became angry and spoke loudly, while he stood toe to toe with Roum, who remained in handcuffs. A videotape of the encounter, which included the sound recording but no corresponding visual depiction, established that in response to Roum, appellant stated repeatedly "What did you say to me?" as he became progressively louder. Roum eventually muttered, "I didn't say nothing." Officers Shymansky and Gallagher testified that they saw appellant strike Roum in the forehead with his forearm three or four times, which caused Roum to fall to the ground. Both officers testified that their attention was focused on appellant and Roum when appellant struck Roum and that their view was unobstructed.3 At trial, appellant testified that, in accordance with MPD operating procedures, he used his forearm to subdue Roum because Roum attempted to headbutt him.4 However, Officer Gallagher testified that he did not see Roum attempt to headbutt appellant before appellant struck Roum.5 Officer Shymansky also testified that he did not see Roum make an aggressive movement before appellant struck him. After the incident, police officers brought Roum to the hospital. Officer Shymansky testified that later that night, when he asked appellant why he struck Roum, appellant responded something akin to "yeah, whatever, I'm sorry."

Following a bench trial, Judge Wynn orally issued her judgment, finding appellant guilty of one count of assault. She sentenced appellant to thirty days, with execution of sentence suspended, followed by a period of three years supervised probation to monitor the defendant's performance of five hundred hours of community service. Appellant filed a Motion to Overturn Conviction or for a New Trial, which the trial court denied without a hearing. Appellant filed timely appeals of the denial of the motion and of his conviction.

II.

A.

We first address appellant's contention that there was insufficient evidence to support his assault conviction. "In a sufficiency challenge we view the evidence in the light most favorable to the government, draw all reasonable inferences in the government's favor, and defer to the factfinder's credibility determinations." Dunn v. United States, 976 A.2d 217, 221 (D.C. 2009) (citation omitted); see also Rivas v. United States, 783 A.2d 125, 134 (D.C. 2001) (en banc) ("A court must deem the proof of guilt sufficient if, after viewing the evidence in the light most favorable to the prosecution, any rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt." (internal quotation marks and citations omitted)). Consequently, "[t]his standard of review places a heavy burden on appellant." Watson v. United States, 979 A.2d 1254, 1256 (D.C.2009) (internal quotation marks and citation omitted).

To prove assault, the government must prove three elements beyond a reasonable doubt: (1) an act by the defendant; (2) "at the time the defendant commits the act, the defendant must have the apparent present ability to injure the victim"; and (3) "at the time the act is committed, the defendant must have the intent to perform the acts which constitute the assault." Dunn, supra, 976 A.2d at 219-20 (internal quotation marks and citation omitted). Here, only the third element is in dispute: whether the evidence established that appellant harbored the intent to assault Roum. The resolution of this issue is primarily contingent upon a credibility contest between appellant and Officer Gallagher, and the probative value of the videotape.6 Appellant argues that the trial court erred by crediting Officer Gallagher's testimony over appellant's testimony because Officer Gallagher's testimony was unreliable and inconsistent. Appellant also argues that the video recording cannot establish the assault occurred because "mere words do not constitute an assault." Dunn, supra, 976 A.2d at 219 (internal quotation marks and citation omitted).

Whereas appellant testified that he struck Roum in response to an attempted headbutt, Officer Gallagher testified that he observed, from close proximity, appellant strike Roum several times without provocation. While Officer Gallagher acknowledged that he might have glanced away momentarily, he was "very certain" that Roum did not provoke the assault. This "[c]onflicting trial testimony is, of course, nothing new and it is the duty of the finder of fact to reconcile such inconsistencies." Lazo v. United States, 54 A.3d 1221, 1230 (D.C.2012). In turn, "[w]e have long held that the trial court is in the best position to observe and assess the demeanor of the witnesses." Poole v. United States, 929 A.2d 413, 415 (D.C. 2007) (internal quotation marks and citation omitted). We decline to "redetermine the credibility" of either witness because the trial judge "had the opportunity to observe their demeanor and form a conclusion." Shepherd v. United States, 905 A.2d 260, 262 (D.C.2006) (internal quotation marks and citation omitted) (accepting the trial judge's determination that the version of events described by the government's witnesses was more credible than that offered by the appellant); see also Hart v. United States, 863 A.2d 866, 873 (D.C.2004) ("Where there are two permissible views of the evidence, the factfinder's choice between them cannot be clearly erroneous." (quoting Anderson v. Bessener City, 470 U.S. 564, 574, 105 S.Ct. 1504, 84 L.Ed.2d 518 (1985))). Therefore, we accept the trial judge's determination that Officer Gallagher was more credible than appellant.

Appellant argues that the videotape cannot support appellant's conviction because "mere words do not constitute an assault." On the recording, appellant repeatedly and aggressively asks Roum: "what did you say to me?" In response, Roum mumbles, "I didn't say nothing." From this exchange, it was not unreasonable for the trial judge to infer that appellant, who was perceptibly angry with Roum for uttering the racial slur, harbored the requisite intent to assault Roum. Moreover, appellant never states anything related to Roum's actions, such as "what did you do?," "stop resisting," or "calm down." Such comments could have suggested that Roum was physically aggressive. As we must "draw all reasonable inferences in the government's favor" on appeal, we accept the trial judge's finding that the audio recording of the altercation corroborates Officer Gallagher's testimony that Roum did not attempt to headbutt appellant. Dunn, supra, 976 A.2d at 221. Thus, there was sufficient evidence to establish that appellant assaulted Roum.

B.

Next, we consider whether the trial court properly addressed appellant's requests for Jencks material.

Lazo, supra, 54 A.3d at 1231 (internal quotation marks and citation omitted). Before the court will require the government to turn over Jencks material to a defendant, the following four prerequisites must be met: "(1) [t]he material must be in the possession of the government; (2) the defense must request the material; (3) the material must constitute a `statement' as defined in the Jencks Act; and (4) the statement must relate to the subject matter of the witness' direct testimony." Id. (internal quotation marks, alterations, and citations omitted). When a defendant requests production of statements pursuant to the Jencks Act, "the trial judge has an affirmative duty, either by interrogation or by in camera inspection, to ascertain whether the statement is one defined by the Act itself as producible material and whether it is in the possession of the government." Bayer v. United States, 651 A.2d 308, 311 (D.C.1994) (internal quotation marks and citation omitted). Therefore, the defendant's burden "`is simply to establish by probative evidence usually on cross-examination of the witness alleged to have given a statement that there is reason to believe that a statutory "statement" may exist.'" Lazo, supra, 54 A.3d at 1232 (emphasis added) (quoting Goldberg v. United States, 425 U.S. 94, 124, 96 S.Ct. 1338, 47 L.Ed.2d 603 (1976) (Powell, J., concurring)). Although the defendant must show more than "speculative possibility," the defendant need not prove that the statement exists. Id. Instead, "counsel need elicit only that the witness was interviewed by an agent of the government, who made notes of the conversation." Johnson v. United States, 800 A.2d 696, 700 (D.C.2002) (internal quotation marks and citation omitted).

We entrust the administration of the Jencks Act to the trial court. Lazo, supra, 54 A.3d at 1231. Therefore, we have "afforded trial courts considerable deference in ruling on Jencks Act issues, which we review for abuse of discretion." Id. (internal quotation marks and citation omitted). However, even if we conclude that the trial court abused its discretion in ruling on a Jencks issue, the error is only grounds for reversal if we also hold that the error was not harmless. Id. at 1235 (citing Lyles v. United States, 879 A.2d 979, 982-83 (D.C.2005)). An error is harmless if we determine, "`with fair assurance, after pondering all that happened without stripping the erroneous action from the whole, that the judgment was not substantially swayed by the error.'" Lazo, supra, 54 A.3d at 1235 (quoting Kotteakos v. United States, 328 U.S. 750, 765, 66 S.Ct. 1239, 90 L.Ed. 1557 (1946)).

Appellant alleges that the trial court abused its discretion by neither ordering the government to disclose Jencks materials nor conducting an evidentiary hearing to determine whether the materials existed pertaining to each of its principal witnesses, Officer Gallagher, Officer Shymansky, and Sergeant Mercier.7 Accordingly, we consider whether Jencks violations occurred with respect to: (1) notes taken by Sergeant Mercier during his interviews with Officer Gallagher; (2) notes taken by the prosecutor during her interviews with Officer Gallagher; and (3) notes taken by Officer Shymansky or by government agents during interviews with Officer Shymansky.

1.

During his cross-examination of Officer Gallagher, defense counsel asked a series of questions about whom Officer Gallagher had discussed the Roum incident with and then requested Jencks materials pertaining to Officer Gallagher because he did not "think that [he had] everything in light of what [he] heard from Officer Gallagher." Although Officer Gallagher testified that he met with the prosecutor and Sergeant Mercier approximately ten times to discuss the case, defense counsel informed the trial court that in response to his Jencks request, the government had only provided a copy of Officer Gallagher's grand jury testimony from March 2007 and Sergeant Mercier's notes from one meeting with Officer Gallagher that took place on March 15, 2007. Defense counsel emphasized, "I'm saying Sergeant Mercier would be at the meetings with Officer Gallagher and would take reports and ... we should have Sergeant Mercier in a full evidentiary hearing about Jencks." At that point, the prosecutor insisted that she had already asked Sergeant Mercier for all of his notes and he had "prepared summaries after the fact, which of course, are not Jencks...."

In response to this Jencks request, the trial judge stated that she did not think that Officer Gallagher had mentioned that Sergeant Mercier had taken notes during their meetings. The trial judge continued: "[The prosecutor] has said that she checked with [Sergeant] Mercier; that she asked him for all his notes and this is what she got. You can ask questions — direct questions about that to make your record." Defense counsel responded: "Okay. That's what I will do." In response to defense counsel's questioning, Officer Gallagher then testified that he remembered Sergeant Mercier "writing stuff down" during the meetings. Specifically:

After this exchange, defense counsel stated: "I want to renew [the Jencks] issue and I will address it when this gentleman is done testifying." However, defense counsel did not specifically raise the Jencks issue again with respect to these notes.

Nevertheless, we conclude that defense counsel's first request for a "full evidentiary hearing," coupled with the testimony elicited from Officer Gallagher, was sufficient to satisfy appellant's burden.8 When Officer Gallagher testified that he observed Sergeant Mercier taking notes during their meetings, defense counsel established that "statutory statement[s] may exist." Lazo, supra, 54 A.3d at 1232 (emphasis added). Doing so triggered the trial court's "affirmative duty" to ascertain "either by interrogation or by in camera inspection," whether Sergeant Mercier did create additional Jencks materials and the whereabouts of such materials. Bayer, supra, 651 A.2d at 311; see also Flores v. United States, 698 A.2d 474, 481 (D.C. 1997) ("We agree that in light of Lainez's testimony at trial that the police took notes of her statement, the trial court should have undertaken an independent Jencks inquiry into the existence and location of notes taken by the police of Lainez's statement."). From the record, it seems that the trial judge accepted the prosecutor's representation that she had requested all notes from Sergeant Mercier and turned them over to appellant. It is, however, immaterial that the prosecutor insisted that the government had already disclosed all of Sergeant Mercier's notes because we have repeatedly held that a trial court may not accept a prosecutor's representation that the government has disclosed all Jencks materials. See Lazo, supra, 54 A.3d at 1235 ("But simply to accept the prosecutor's representation without conducting any independent inquiry at all into the existence of potential Jencks material from a second officer is plainly not an appropriate evidentiary inquiry under the circumstances."); Johnson, supra, 800 A.2d at 701 (The "prosecutor's lack of awareness of any notes did not establish that they did not exist or could not be found.").

We are not persuaded by the government's contention that the trial court sufficiently accommodated appellant's request for an evidentiary hearing by allowing appellant to ask Officer Gallagher questions pertaining to Sergeant Mercier's note-taking during their meetings. This line of questioning merely elicited Officer Gallagher's testimony that Sergeant Mercier took notes during their meetings; it triggered the trial court's duty to inquire further but did not settle the issue. The government also argues that the prosecutor provided additional Jencks material to appellant before Sergeant Mercier took the stand one month later to testify about his measurements of the interview room. However, the record does not indicate what Jencks material the government provided, and even if it did, such disclosure did not absolve the trial court of its "affirmative duty" to determine whether these materials fulfilled appellant's request for all of Sergeant Mercier's notes taken during his meetings with Officer Gallagher. Bayer, supra, 651 A.2d at 311.

Finally, the government asserts that appellant eventually had the opportunity to question Sergeant Mercier about his notes, when he testified a month after Officer Gallagher. Yet, the trial court's duty to investigate was triggered when defense counsel requested the notes during Officer Gallagher's testimony. See id. (concluding that, at the point defense counsel moved for production of officer's notes and established the existence of these notes, "the trial court should have investigated whether the police officer's notes qualified as a `statement'"). To require otherwise, by allowing cross-examination to occur without determining whether the statements recorded by Sergeant Mercier existed, would defeat the purpose of the Jencks Act, which seeks to "`aid[ ] the search for truth by facilitating the impeachment'" of Officer Gallagher. Lazo, supra, 54 A.3d at 1231 (quoting Frye v. United States, 600 A.2d 808, 810 (D.C.1991)). Moreover, expecting defense counsel to wait a month to determine whether Sergeant Mercier had taken notes that included Jencks statements from Officer Gallagher would both shift the burden of inquiry from the trial court to appellant and would require recalling Officer Gallagher as a witness, unnecessarily delaying the trial.

Accordingly, because we hold that the trial court erred by failing to conduct a hearing regarding the existence of Sergeant Mercier's notes, we must determine whether the error was harmless. To evaluate this error without the alleged notes,

Johnson, supra, 800 A.2d at 701 n. 4 (internal quotation marks, citations, and brackets omitted). In Lazo, we found that the trial court's error was not harmless because the missing notes were recorded during interviews of the complaining witness, G.F., whose testimony was significant in proving the government's case. 54 A.3d at 1236-37. We were further persuaded that the error was not harmless by G.F.'s "inconsistent testimony, the conflict between G.F.'s testimony and that of other witnesses, and the suggestion that G.F. had motive to fabricate." Id. at 1237. Similarly, here, Officer Gallagher's eyewitness account was critical to the trial court's judgment, it contradicted appellant's own testimony, and at trial and in his brief, appellant argued that Officer Gallagher had motive to fabricate his testimony to avoid punitive action by the government for his own role in Roum's injuries. Officer Gallagher's testimony was especially important because the court did not credit the testimony of Officer Shymansky or appellant, who were the only other direct witnesses to the assault. Moreover, appellant did not have access to any other evidence of statements made by Officer Gallagher during these interviews because the only other participant, the prosecutor, did not take notes. Cf. Moore v. United States, 657 A.2d 1148, 1150 (D.C.1995) (finding error harmless "because the information contained in the [missing report] was also available in three other documents which had already been turned over to defense counsel"). Thus, "assum[ing] the worst," appellant was unable to impeach Officer Gallagher with statements that he possibly made during his repeated meetings with the prosecutor and Sergeant Mercier. Johnson, supra, 800 A.2d at 701 n. 4. Consequently, we hold that the trial court's failure to investigate whether Sergeant Mercier's notes contained Jencks statements was not harmless.

We remand this discrete issue to the trial court to conduct an evidentiary hearing to determine whether Sergeant Mercier took notes during his interviews of Officer Gallagher and whether such notes constitute Jencks statements. If so, the trial court must determine whether the failure to disclose the Jencks materials was harmless error. Unlike our appellate review for harmless error, which entailed the decision of whether the government's case could stand without Officer Gallagher's testimony, "the trial court can find non-production of the statements harmless, however, only if it finds that the statement could not have been used to discredit [Gallagher]." Bayer, supra, 651 A.2d at 312 n. 4. If the failure to produce these statements was not harmless, the trial court must vacate appellant's conviction and order a new trial. See id.

2.

Appellant also argues that the prosecutor did not provide notes from her interviews with Officer Gallagher to defense counsel, in violation of the Jencks Act. This argument is without merit. When defense counsel articulated this concern at trial, the prosecutor stated that she deliberately did not take notes during witness interviews to avoid creating Jencks material, the court observed, "that is what one would expect of an experienced prosecutor," and defense counsel replied "I think it is." Defense counsel then clarified that he would "focus [his] attention on Sergeant Mercier" and did not raise the issue of the prosecutor's notes again. "[A]bsent compelling evidence to the contrary, when a court receives an assurance directly from the prosecutor — an officer of the court — that she did not take any notes during her interview with a witness, the court satisfies its duty of independent inquiry to determine whether or not the conditions of the Jencks Act have been satisfied." Lazo, supra, 54 A.3d at 1238 (internal quotation marks, brackets, and citation omitted). Whereas defense counsel elicited testimony from Officer Gallagher establishing that Sergeant Mercier may have created Jencks materials that the government did not disclose, there was no testimony suggesting that the prosecutor also created Jencks materials during her meetings with Officer Gallagher and Sergeant Mercier. In light of the prosecutor's assurance that she recorded no Jencks statements, defense counsel's acceptance thereof, and the lack of any compelling evidence to the contrary, we conclude that the court did not abuse its discretion by denying appellant's request for the prosecutor's notes.

3.

At trial, Officer Shymansky testified that despite making a "diligent" effort to find his handwritten notes, which he transcribed during a meeting with the prosecutor, they were lost. Appellant moved to strike Shymansky's testimony, arguing that his claim "smacks of bad faith" or "gross negligence." The prosecutor responded that it made no sense that Shymansky would have candidly reported their existence if he had intentionally destroyed them. The trial court refused to strike Shymansky's testimony, finding no evidence of bad faith. Instead, the court allowed appellant to cross-examine Shymansky to the extent that appellant desired.

Regardless of whether Officer Shymansky's personal notes constituted Jencks statements, if the government was required to disclose these notes, the failure to do so was harmless error. Lazo, supra, 54 A.3d at 1235. Defense counsel effectively impeached Officer Shymansky regarding the extent to which he was able to observe the altercation between appellant and Roum. Any error was harmless because the trial judge stated when delivering her judgment that "even if his testimony had been stricken, the absence of that testimony would not have made a difference in my verdict." Nor did we rely on Officer Shymansky's testimony in finding that there was sufficient evidence to support appellant's conviction. Therefore, we are satisfied that "the judgment was not substantially swayed" by the error, if any, and the missing Shymansky notes provide no basis for remand or reversal. See id.

C.

Finally, we evaluate whether the trial court erred by denying appellant's Motion to Overturn Conviction or for a New Trial based on newly discovered evidence. "On a defendant's motion, the Court may grant a new trial to the defendant if the interests of justice so require." Super. Ct.Crim. R. 33. "To succeed on a motion for a new trial based on newly discovered evidence, the movant has to show that: (1) the evidence is newly discovered; (2) the moving party was diligent in seeking to obtain the evidence; (3) the evidence is material to the issues involved and not merely cumulative or impeaching; and (4) it is of a nature that it would probably produce an acquittal." Ingram v. United States, 40 A.3d 887, 901 (D.C. 2012) (internal quotation marks and citations omitted). "The trial judge has discretion to grant or deny a motion for a new trial, and our review is confined to determining whether there has been an abuse of discretion." Id. (citation omitted).

Appellant argues that the trial court abused its discretion by denying, without a hearing, his motion for a new trial based on Officer Gallagher's post-trial testimony at the adverse action hearing before the MPD Disciplinary Board (the "hearing"). During the hearing, Officer Gallagher testified that it was "possible" that he missed a headbutt by Mr. Roum. The following is the most important part of Officer Gallagher's testimony from the hearing:

Upon consideration of this testimony, the trial judge denied appellant's motion because the evidence was merely cumulative and impeaching, noting that it would not have resulted in an acquittal if it had been presented at trial. In doing so, the judge found that Officer Gallagher's statements at the hearing were "not significantly different" from the statements he made at trial. We agree.

While being cross-examined at trial, Officer Gallagher stated: "I would say I'm paying attention. I mean, I might have glanced here and there a couple of times, but for the most part, yes, I was paying attention ... I don't think I missed a move." Although he testified that he was "very certain" that he never saw Roum provoke appellant, Officer Gallagher never testified that an attempted headbutt could not have occurred. Indeed, by conceding that he "might have glanced here and there a couple of times," Officer Gallagher's trial testimony did not foreclose the possibility that he missed a headbutt.

During the subsequent hearing, Officer Gallagher did not change his version of events. Rather, as he had stated during cross-examination, Officer Gallagher acknowledged that he did look away at one point, and that it was possible that he missed something. Therefore, Officer Gallagher was already impeached on the same basis at trial. Indeed, the trial court already had the opportunity to consider the possibility that the headbutt had occurred, but Officer Gallagher had not seen it. For this reason, the evidence from the hearing was both cumulative and impeaching, thereby failing to fulfill the third prong of the test for admitting newly discovered evidence. Prophet v. United States, 707 A.2d 775, 778 (D.C.1998) ("Impeaching evidence is evidence that is relevant only because it undermines or casts doubt on the credibility of a witness."); see also Gaither v. United States, 759 A.2d 655, 665 (D.C.2000), amended by Gaither v. United States, 816 A.2d 791 (D.C.2003) (declining to consider new evidence undermining eye witness's credibility when eye witness had already been impeached at trial).

Furthermore, Officer Gallagher's testimony during the hearing did not fulfill the fourth prong requiring that the evidence be "of such a nature that an acquittal would likely result from its use" because Officer Gallagher maintained his position from trial that, from what he did see, appellant was the aggressor. As discussed above, the trial judge did not credit appellant's testimony that Roum headbutted him, and we defer to her finding. Finally, appellant's conviction was also supported by the audio recording, which revealed appellant's verbally aggressive behavior during his altercation with Roum.

Alternatively, appellant argues that the trial court abused its discretion by denying his motion without conducting an evidentiary hearing. Yet, we have recognized that the trial court may decide a defendant's motion without an evidentiary hearing if the claims can be disposed of by review of the record. See Bell v. United States, 871 A.2d 1199, 1201 (D.C.2005); see also Busey v. United States, 747 A.2d 1153, 1168 (D.C.2000) (affirming denial of motion for new trial without a hearing because "[e]ven assuming that the witness would have testified credibly ... that would not refute directly the substantial evidence" against defendant). Unlike the appellants' motions for new trials based on newly discovered evidence in Arrington v. United States, 804 A.2d 1068, 1077 (D.C. 2002), or Thomas v. United States, 942 A.2d 1180, 1184-85 (D.C.2008), appellant here did not urge the trial court to consider the testimony of a new witness, whose credibility the trial court had yet to evaluate. Instead, the trial judge had ample opportunity to evaluate the credibility of Officer Gallagher during his testimony, which spanned over many hours. Cf. Thomas, supra, 942 A.2d at 1185 (finding the trial court "abused its discretion by making a credibility determination based on the double hearsay affidavit ... without giving [the new witness] the opportunity to testify under oath and without observing her character and demeanor firsthand"). Moreover, defense counsel had questioned Officer Gallagher extensively during trial about his observation of the altercation between appellant and Roum. Accordingly, we hold that the trial court did not abuse its discretion in denying appellant's motion for a new trial without conducting a hearing.

III.

For the foregoing reasons, we remand to the trial court to conduct an evidentiary hearing to determine whether the government failed to disclose Jencks materials created by Sergeant Mercier and if so, whether the failure to do so was harmless. We affirm in all other respects.

So ordered.