FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA, 

No. 06-10173 Plaintiff-Appellee,

D.C. No.

v.  CR-05-00519-1-

OSCAR ARMANDO HERNANDEZ- DCB

ACUNA,

OPINION Defendant-Appellant. 

Appeal from the United States District Court

for the District of Arizona

David C. Bury, District Judge, Presiding

Argued and Submitted

July 10, 2007—San Francisco, California

Filed August 16, 2007

Before: David R. Thompson, Pamela Ann Rymer, and

Raymond C. Fisher, Circuit Judges.

Opinion by Judge Rymer

9985
COUNSEL

Raul A. Miranda, Tucson, Arizona, for defendant-appellant

Oscar Armando Hernandez-Acuna. 

George Ferko, Assistant United States Attorney, Christina M.

Cabanillas, Appellate Chief, and Paul K. Charlton, United

States Attorney, Tucson, Arizona, for appellee the United

States. 

OPINION

RYMER, Circuit Judge: 

Oscar Hernandez-Acuna appeals his conviction and sentence for conspiracy and possession of marijuana with the

intent to distribute. The issue is whether the district court’s

rejection of the magistrate judge’s recommendation to suppress evidence without conducting its own evidentiary hearing violated due process. In this case, even if the court should

UNITED STATES v. HERNANDEZ-ACUNA 9987
have held a de novo hearing, the same witnesses who testified

before the magistrate judge at the suppression hearing testified at trial about why they stopped and searched HernandezAcuna’s car. Hernandez-Acuna asked the court to consider its

ruling again after the close of evidence. In these circumstances, we conclude that remand for another hearing is not

required. Accordingly, we affirm. 

I

On the night of February 19, 2005, Border Patrol Agents

John Howard, Luis Santiesteban, and Anthony Ortiz were stationed in two marked vehicles next to State Road 83 near

Vail, Arizona, on the lookout for smugglers. Howard and Santiesteban testified at the suppression hearing and at trial that

they saw a sedan and a pickup truck approaching their position; they believed the two vehicles were driving in tandem;

they noticed that both vehicles had temporary registration

tags, which smugglers’ vehicles frequently display; and they

thought the rigid reaction to their floodlights of the driver

(Hernandez-Acuna) and passenger in the sedan was unusual.1

Santiesteban pulled onto the road behind the truck, where he

observed bundles that he believed were marijuana. He radioed

this to Howard, who was following the sedan. Santiesteban

stopped the truck and Howard stopped the sedan. Upon

inquiry they discovered that both vehicles were registered to

the same address and to owners with similar names, and that

both had been purchased from the same dealership within

days of each other. The agents then placed Hernandez-Acuna

under arrest. 

Hernandez-Acuna was indicted in the District of Arizona

on charges of conspiracy and possession with intent to distribute approximately 302 kg of marijuana in violation of 21

U.S.C. §§ 841 and 846. He filed a motion to suppress evidence seized by the Border Patrol, including in particular the

1Ortiz was indisposed and did not testify on either occasion. 

9988 UNITED STATES v. HERNANDEZ-ACUNA
registration documents that linked his car to the truck in

which the marijuana was found. The motion was referred to

a magistrate judge, who recommended suppression. He concluded that the government had not set forth an objective and

rational basis to support the conclusion that the sedan and

truck were traveling together. 

The government objected to the Report pursuant to 28

U.S.C. § 636(b)(1), arguing that the magistrate judge’s analysis was inconsistent with United States v. Arvizu, 534 U.S.

266 (2002). The district court disagreed with the magistrate

judge’s report and declined its recommendation. In its view,

under the totality of the circumstances, the agents had a reasonable suspicion that the sedan was traveling in tandem with

the truck. 

Howard and Santiesteban testified during the two-day trial,

as they had at the evidentiary hearing, about the stop and

search of Hernandez-Acuna’s sedan. Defense counsel crossexamined extensively, and sought to impeach the agents

based in part on the transcript of proceedings before the magistrate judge. At the close of evidence, Hernandez-Acuna

moved for reconsideration of his earlier motion to suppress,

which the district court denied. The jury returned a guilty verdict. 

Hernandez-Acuna timely appeals the district court’s failure

to conduct a de novo evidentiary hearing.2

2Hernandez-Acuna asserts a violation of the Fifth Amendment, not the

Fourth Amendment. The Fourth Amendment is in play only to the extent

that the Fifth Amendment guarantees that the merits of Fourth Amendment challenges will receive an appropriate hearing. Otherwise,

Hernandez-Acuna has waived any claim that the order denying his motion

to suppress was infirm under substantive Fourth Amendment law by failing to develop any argument with respect to it. 

UNITED STATES v. HERNANDEZ-ACUNA 9989
II

We first addressed the question whether a district court

must conduct its own evidentiary hearing before rejecting a

magistrate judge’s recommendation to suppress evidence in

United States v. Bergera, 512 F.2d 391 (9th Cir. 1975). At

issue there was the reach of our decision in Campbell v.

United States District Court for the Northern District of California, 501 F.2d 196 (9th Cir. 1974), which had upheld the

constitutionality of the Federal Magistrates Act, 28 U.S.C.

§ 636, against an as applied challenge under Article III of the

Constitution. Campbell had established that it is consistent

with Article III for a magistrate judge to conduct a suppression hearing, provided that the district judge makes the ultimate determination granting or denying the motion. 501 F.2d

at 205. Bergera limited the scope of this rule, holding that it

did not extend to a case in which the magistrate judge recommended granting a motion to suppress and the district court

subsequently denied the motion based on the record of the

suppression hearing conducted by the magistrate judge. 512

F.2d at 392-94. 

[1] Subsequently, the Supreme Court’s decision in United

States v. Raddatz, 447 U.S. 667 (1980), confirmed the correctness of Campbell’s holding that magistrate judges may conduct suppression hearings. The Supreme Court recognized

that the issue has a due process dimension in addition to the

Article III concerns that we addressed in Campbell, but it concluded that use of magistrate judges to conduct suppression

hearings comported with the Due Process Clause as well as

with Article III. 447 U.S. at 680, 683-84. However, the Court

clarified that its decision did not reach the issue of the process

required when a district judge rejects a magistrate judge’s

proposed findings on credibility. Id. at 681 n.7. For a district

judge to reject a magistrate judge’s dispositive findings on

credibility without himself hearing the witnesses’ testimony

could, the Court noted, “give rise to serious questions.” Id.

Consequently, we reaffirmed in United States v. Ridgway, 300

9990 UNITED STATES v. HERNANDEZ-ACUNA
F.3d 1153 (9th Cir. 2002), that a district court errs when it

does not conduct a de novo evidentiary hearing if it rejects the

credibility finding of a magistrate judge who recommends

granting a motion to suppress. Id. at 1156-57. We further clarified that this rule encompasses all credibility findings, without any limitation to findings based on a witness’s demeanor,

id. at 1157, but we did not decide whether the same rule

applies to a reversal based on findings other than credibility,

id. at 1157 n.3. 

[2] Here, the magistrate judge did not make an express

credibility finding, nor, unlike Ridgway, did the district court

expressly reject findings with respect to the agents’ credibility. However, the magistrate judge’s Report does state that he

“finds it troubling that upon the Court’s open-ended questioning, the agents’ responses as to why they believed the vehicles

were connected indicates that the issue of the temporary

plates did not arise until after the agents reviewed the registration once the Defendant was stopped, i.e., the confirmation

alone that the truck was transporting marijuana precipitated

the stop.” In context, this statement is ambiguous. It could be

taken to implicate the agents’ credibility — or it could be

taken as an “aside” that was unnecessary to the magistrate

judge’s legal judgment that the presence of lawful temporary

plates on two vehicles being driven in a lawful manner is not

a basis for believing that the vehicles are being driven

together. We cannot tell how the district court interpreted the

magistrate judge’s statement, but the court’s order appears to

assume that the agents factored their observation of temporary

license plates into the reasonable suspicion calculus. To the

extent the magistrate judge’s statement was intended as a

reflection on the agents’ credibility, it should not have been

rejected absent live testimony upon which to do so. 

[3] We need not wrestle further with the ambiguity, however, because in this case if there were error, it was cured by

the instant replay that occurred at trial. As the Supreme Court

indicated in Carroll v. United States, 267 U.S. 132, 162

UNITED STATES v. HERNANDEZ-ACUNA 9991
(1925), and we echoed in United States v. Sanford, 673 F.2d

1070, 1072 (9th Cir. 1982), denial of a motion to suppress

may be sustained on the basis of evidence presented at trial.

The reason is: “[t]he whole matter was gone into at the trial,

so no right of the defendants was infringed.” Carroll, 267

U.S. at 162. Howard and Santiesteban were the only witnesses

at the suppression hearing, and both testified at trial about

when and why they thought Hernandez-Acuna’s sedan was

linked to the truck. In this, Hernandez-Acuna’s situation is

unlike Bergera, where one witness who testified at the suppression hearing did not testify at trial. Howard and Santiesteban were examined and cross-examined about all aspects of

the stop, including the temporary tags and what they signified.

Their credibility was attacked. The district judge was able to

see and hear their live testimony and to observe their demeanor. He could evaluate their trustworthiness and the weight of

the factors they considered for himself. In short, the judge had

the opportunity to do exactly what he would have done had

he held an evidentiary hearing. Of course it cannot be gainsaid that trials serve a different function from evidentiary

hearings; but judges can, and occasionally do, revisit their

pretrial rulings as a trial runs its course and testimony or

exhibits are adduced that put threshold decisions in a different

light. Moreover, there is no question the parties and the court

understood that suppression was on the table; HernandezAcuna specifically asked for the court to rule again. 

[4] In these circumstances, we conclude that there is no

need for another evidentiary hearing. 

AFFIRMED. 

9992 UNITED STATES v. HERNANDEZ-ACUNA