Defendant Sixto Mireles appeals from a conviction of possession of marijuana with intent to distribute, in violation of 21 U.S.C. § 841(a)(1). He contends that the district court erred in denying his motion to suppress the evidence obtained as a result of an allegedly unlawful search conducted at the Falfurrias checkpoint. The second ground of error asserted is that the prosecutor's questions and argument impermissibly commented on the exercise of defendant's constitutional right to remain silent after arrest. Finally, defendant claims that there was insufficient evidence that defendant knowingly transported the marijuana. We affirm.

Defendant was driving a two-ton truck when he was stopped at a Border Patrol checkpoint 7 miles south of Falfurrias, Texas. The Border Patrol Agent, Officer Edwards, questioned Mireles about his citizenship. After determining that defendant was a citizen of the United States, Edwards asked Mireles if there was anyone in the box part of the truck. The Agent testified that Mireles became "physically nervous" when the rear of the truck was mentioned, and that defendant's response to his question was that there was "no one back there, just my personal furniture". Mireles was then asked to drive to the secondary inspection area and to open the back of the truck. Defendant complied, and when the rear of the van was opened by Mireles, the Agent discovered that the van was partially loaded with furniture, and that there were mothballs scattered on the floor. In addition, Officer Edwards identified some marijuana seeds and pieces of leaves in the cracks and on the floor of the van. Despite the mothballs, Edwards detected the odor of marijuana. After examining the interior of the van, and comparing it with the exterior dimensions, Agent Edwards suspected that there was a concealed compartment in the front of the van. He then removed the plywood panel and discovered 1805 pounds of contraband. At that time defendant was advised of his Miranda rights, and placed under arrest. After defendant acknowledged that he fully understood his rights, Edwards asked him if the marijuana in the secret compartment was his. According to Officer Edwards, Mireles stated that the marijuana was not his, that he had not known of its presence, and that defendant had borrowed the truck from his uncle to move defendant's furniture to his new residence.

After discovering the contraband and arresting Mireles, Edwards notified Agent Havens to take defendant and the contraband into custody. Havens testified that the furniture in the van consisted of an apparently inoperative small refrigerator, a clothes washer and dryer, part of a bedstead, and some miscellaneous pieces. Agent Havens stated that after he had returned to the Corpus Christi District Office, he asked defendant if the furniture belonged to him, and Mireles responded that it did not.

Defendant Mireles testified at trial. His defense was based on his purported lack of knowledge that nearly a ton of marijuana was concealed in the rear of the truck. According to defendant, a man named Guadalupe Rivas paid him $150 to move Rivas' furniture from San Juan to Port Lavaca. Defendant stated that he helped load the furniture into the truck, but that he was not aware of the marijuana in the concealed compartment. Mireles testified that he first met Guadalupe Rivas, also known as Tio Rivas, at a garage owned by defendant's godfather. Defendant admitted that he had not talked with Rivas for nearly a year prior to the request to deliver the furniture. Mireles' version of the encounter at the Falfurrias checkpoint contradicted Agent Edwards' testimony that defendant stated that the furniture in the rear of the truck belonged to him. Defendant conceded that after the contraband was discovered he might have mentioned something about an uncle, but that the mention of an uncle was intended to be a reference to Tio Rivas, as "Tio" means "uncle" in Spanish.

Defendant's counsel made a motion to suppress evidence of statements made by defendant and physical items obtained or discovered as a result of the search of the truck Mireles was driving. In the motion it was contended that the absence of probable cause or a warrant for the arrest of defendant or the search of the truck invalidated both the stop and the search of the vehicle. Before the jury was seated and any evidence had been taken, defendant's counsel asked the district judge whether the motion to suppress would be carried with the trial of the case. The judge responded that it would be, and inquired whether it was a checkpoint case. The prosecutor informed the court that it was a checkpoint case, and the trial judge stated that he would take judicial notice of the physical characteristics of the checkpoint and would sign an order to that effect, as was his practice in such cases. Defendant's counsel stated he had no objection, and an order was filed the same day. The order included a description of a checkpoint located 16 miles south of Falfurrias, entered in a previous criminal action also presided over by District Judge Cox, as well as Supplemental Findings of Fact and Conclusions of Law in that case, which noted that the permanent checkpoint 16 miles from Falfurrias was the functional equivalent of the border.1 The checkpoint involved in this case is 7 miles from Falfurrias.

In his opening statement defendant's counsel agreed with the prosecutor that "the only question here before us today is that of knowledge". At trial, defendant testified that he was unaware of the marijuana contained in the concealed compartment. Defendant's attorney stated that he had no objection to the admission of a photograph of the contraband and a stipulation as to its substance and amount, nor did he object to the admission of any of the evidence previously sought to be suppressed. Counsel never requested a ruling on the motion to suppress, or sought a directed verdict of acquittal, and no ruling was ever made. It is therefore clear that defendant effectively abandoned the motion to suppress, and relied instead on his asserted innocence.2

The appropriate inquiry at this juncture is whether admission of the fruits of the stop3 and the search was nevertheless plain error. See Fed.R.Crim.P. 52(b); United States v. Brown, 5 Cir., 1977, 555 F.2d 407, 420, cert. denied 46 U.S.L.W. 3541 (Feb. 27, 1978). We conclude that no plain error was committed. Defendant, a part-time student at Texas A & I, never objected to Agent Edwards' request to open the rear of the truck. Officer Edwards testified that Mireles was courteous at all times, and Agent Havens stated that defendant was cooperative. As the contraband was hidden in a concealed compartment at the front of the van, and the van was loaded with furniture as he had told the officers, it was entirely possible that a cursory inspection would not be incriminating. Cf. United States v. Hall, 5 Cir., 1978, 565 F.2d 917, 920-21 (where the court found consent to a search of an automobile trunk that uncovered a sawed-off shotgun sheathed in a billiard cue case). However, the marijuana debris recognized by the experienced officer, the presence of mothballs4 and the recognizable odor of marijuana alerted him to the possible presence of a larger amount of contraband in the truck, and provided the agent with probable cause to search. See United States v. Marez, 5 Cir., 1978, 569 F.2d 275; United States v. Faulkner, 5 Cir., 1977, 547 F.2d 870 (where the discovery of marijuana debris furnished probable cause to search the vehicle). Under the circumstances of this case we find consent to the opening of the rear of the truck,5 and no plain error in the admission of the evidence.6

Defendant argues that certain of the prosecutor's questions and part of his closing argument impermissibly commented on his right to refuse to speak after he had been taken into custody and been read the Miranda warnings. Miranda v. Arizona, 384 U.S. 436, 467-73, 86 S. Ct. 1602, 1624-27, 16 L. Ed. 2d 694 (1966). Reliance for this position is placed principally on Doyle v. Ohio, 426 U.S. 610, 96 S. Ct. 2240, 49 L. Ed. 2d 91 (1976) and two recent Fifth Circuit decisions implementing Doyle : United States v. Luna, 5 Cir., 1976, 539 F.2d 417; and United States v. Harp, 5 Cir., 1976, 536 F.2d 601. A comparison of the circumstances of the present case with those in Doyle decisively shows that defendant's reliance is misplaced, and that there was no impropriety in the prosecutor's questions and argument.

In Doyle the defendants were silent after the Miranda warnings were given.7 At trial they offered an exculpatory version of the marijuana transaction that was the subject of the prosecution. The government sought to undercut the defendants' version by asking each defendant why he had not told the police the exculpatory explanation after arrest. The Supreme Court held that this impeachment by the use of post-arrest silence was fundamentally unfair and a deprivation of due process. According to the majority, "every post-arrest silence is insolubly ambiguous because of what the State is required to advise the person arrested," 426 U.S. 610, 617, 96 S. Ct. 2240, 2244, 49 L. Ed. 2d 91 (1976), and therefore the use of a post-Miranda warning silence by cross-examining a defendant regarding his failure to explain his alleged innocence is impermissible and prejudicial. Both Luna and Harp were simple applications of Doyle to prosecutorial argument that sought to impeach exculpatory explanations offered by defendants by calling attention to the failure of defendants to assert their innocence after arrest and the giving of the Miranda warnings.

In the present case the prosecutor asked defendant on cross-examination if he had not told the Agents about Guadalupe Rivas, and arguably called attention to such failure in his closing argument.8 However, the significance of these questions and statements can only be understood in the proper context. At trial defendant testified that he was not aware of the marijuana concealed behind the paneling in the front of the van, and that he was merely moving furniture for Guadalupe Rivas, also known as "Tio" Rivas. Defendant testified that after his arrest he might have mentioned something about an uncle, and that this was a reference to "Tio" Rivas. Agent Edwards testified that after defendant was given the Miranda warnings, Mireles stated that he had borrowed the truck from his uncle to move Mireles' furniture, and had also denied any knowledge of the contraband.

Thus, a crucial disputed issue in this case was the inconsistency between Mireles' exculpatory story at trial and the Agent's testimony that before the arrest defendant claimed that the furniture was his, and after arrest that he had borrowed the truck from his uncle to move defendant's furniture. Defendant's silence was in no way at issue. Instead, the government was concerned with the inconsistencies as to ownership of the furniture, and whether the truck was borrowed from his uncle or whether it was being driven for pay for Guadalupe Rivas. Defendant's failure to mention Guadalupe Rivas either before or after his arrest bolstered the Agent's testimony that defendant claimed that the furniture was his and that the truck was borrowed from his uncle. Therefore, the prosecutor's questions and argument were not an impeachment by silence, as in Doyle, but merely an effort to impeach by prior statements that were inconsistent with defendant's testimony at trial. There is no "insoluble ambiguity" of silence as noted in Doyle, since defendant Mireles waived his right to remain silent, and denied knowledge of the presence of the contraband after his arrest. Doyle's protection of the right to remain silent does not apply to cross-examination and argument concerning a defendant's exculpatory explanation given after the Miranda warnings.

Finally, defendant contends that the evidence of his knowledge of the presence of the contraband in the truck was insufficient to support his conviction. Defendant's counsel failed to move for a directed verdict, and therefore our review is limited to plain error. See United States v. Francis, 5 Cir., 1973, 487 F.2d 968, 972, cert. denied 416 U.S. 908, 94 S. Ct. 1615, 40 L. Ed. 2d 113 (1974). We find no plain error in this case.

The exculpatory story offered by defendant was contradicted by Agent Edwards' testimony regarding Mireles' statements after his arrest. Officer Edwards stated that defendant said that his personal furniture was in the van, and that he had borrowed the truck from his uncle. Agent Havens testified that Mireles later stated that the furniture was not his, and defendant claimed that his mention of an "uncle" was in fact a reference to Tio Rivas. Of course, the evidence must be taken in the light most favorable to the government. See Glasser v. United States, 315 U.S. 60, 62 S. Ct. 457, 86 L. Ed. 680 (1942). Defendant's explanation of his innocence rested almost entirely on his own testimony, which the jury could reasonably have chosen not to believe. As defendant was the sole occupant and the driver of a truck loaded with nearly a ton of contraband, the jury's verdict of guilty was supported by substantial evidence and was not plain error.

AFFIRMED.

THORNBERRY, Circuit Judge, specially concurring:

Although I join in Judge Ainsworth's able opinion, I write briefly to emphasize the limited nature of the court's holding and the proper application of the harmless error rule in the context of comments on post-arrest silence.

Miranda itself makes clear that "the mere fact that (a defendant) may have answered some questions or volunteered some statements on his own does not deprive him of the right to refrain from answering further inquiries." Miranda v. Arizona, 384 U.S. 436, 445, 86 S. Ct. 1602, 1612, 16 L. Ed. 2d 694 (1966). See also Booton v. Hanauer, 541 F.2d 296 (1 Cir. 1976); United States v. Williams, 181 U.S.App.D.C. 188, 556 F.2d 65, cert. denied, 431 U.S. 972, 97 S. Ct. 2936, 57 L. Ed. 2d 1070 (1977). Accordingly, the rule of Doyle v. Ohio, 426 U.S. 610, 96 S. Ct. 2240, 49 L. Ed. 2d 91 (1976), applies when the prosecutor comments on the defendant's failure to provide a post-arrest exculpatory story after offering other information to the arresting officers. See Booton, supra. It is equally clear that Doyle is inapplicable where the defendant does not remain silent but "attempt(s) to explain at length" his version of the incident. United States v. Berdick, 555 F.2d 1329, 1331 (5 Cir. 1977).

The instant case is not one in which a defendant who answered certain post-arrest questions, without offering an exculpatory story, is impeached at trial with his failure to have provided such an explanation after his arrest. Rather, Mireles told the arresting officer that he had borrowed the truck from his uncle to move his own furniture to a new residence. At trial, however, he testified that one Rivas had hired him to move the furniture, and the prosecutor was free to impeach that testimony with Mireles' prior inconsistent explanation.

In footnote 8 of the court's opinion, Judge Ainsworth discusses briefly the harmless error rule in the Doyle setting, suggesting that even if the prosecutor's comments and questions in the instant case were improper, they were mild, ambiguous, and harmless. However, we have previously indicated that ambiguity alone does not save such statements from the application of the Doyle rule, United States v. Stevens, 538 F.2d 1203 (5 Cir. 1976), and warned that the "infusion of 'harmlessness' into error must be the exception, and the doctrine must be sparingly employed" in this context. Chapman v. United States, 547 F.2d 1240, 1250 (5 Cir.), cert. denied, 431 U.S. 908, 97 S. Ct. 1705, 52 L. Ed. 2d 393 (1977). Obviously, the best course is for prosecutors to "scrupulously avoid all reference to or use of (the) accused's assertion of his right to remain silent." United States v. Wycoff, 545 F.2d 679, 682 (9 Cir. 1976), cert. denied, 429 U.S. 1105, 97 S. Ct. 1135, 51 L. Ed. 2d 556 (1977).