Opinion by Judge MICHAEL DALY HAWKINS: Dissent by Judge PREGERSON

Dr. Samson Dubria (“Dubria”), a California state prisoner, appeals the district court’s denial of his federal petition for a writ of habeas corpus pursuant to 28 U.S.C. § 2254 . This matter was heard originally before a three-judge panel of this court. We accepted the case for en banc review and now affirm the district court. Our jurisdiction is pursuant to 28 U.S.C. § 1291 .

BACKGROUND

Dubria was found guilty following a jury trial of first degree murder, rape by the use of drugs, and administering a drug in order to enable and assist himself to commit a felony. Dubria was given a mandatory sentence of life in prison without the possibility of parole. Following the denial of his consolidated direct and collateral appeals in state court, Dubria sought habe-as relief in district court.

The relevant events began in 1990 when Dubria became friends with Jennifer Klap-per (“Klapper”) while the two were coworkers at an Ohio hospital. Their rela *998 tionship was not romantic. Klapper had stated that she was not physically attracted to Dubria and, at the time of her death, she was romantically involved with another man with whom she was discussing marriage. In the spring of 1991, Dubria invited Klapper to attend his class reunion in California. Klapper was a television and movie fan and did not have the financial means to take a trip to California on her own. She also expressed reservations about the invitation. She told a friend that she felt uncomfortable about going on the trip because she did not know what Dubria expected from her. She also told her boyfriend that she did not want to be away from him. Klapper’s sister overheard a telephone conversation in which Klapper told Dubria that their relationship was platonic and that she had a boyfriend. Further, she told Dubria that if he expected to have physical relations while on the trip, she would have to cancel her plans to go.

Dubria flew to California alone and in advance of Klapper and then picked her up at the airport several days later. The pan-spent the next few days touring Southern California, spending their evenings at the home of Dubria’s parents and sleeping in separate rooms. On August 15,1991, after watching a taping of the Johnny Carson Show, they planned on camping overnight at the San Elijo State Beach Campground between Los Angeles and San Diego. Instead of camping out, the pair checked into the Allstar Inn in Carlsbad, California.

At about 8:09 a.m., Carlsbad police responded to a 911 call at the Allstar Inn. Klapper was lying unconscious on the bed closest to the door. She had no pulse and was not breathing. Dubria and a police officer administered CPR. Firefighters and paramedics arrived shortly thereafter and were able to restore some electrical activity in Klapper’s heart, but not a normal beat. Neither the police nor any of the emergency personnel smelled a chemical odor in the room. Klapper was immediately transferred to a local hospital where further attempts to revive her were unavailing. Emergency room physicians pronounced Klapper dead at 3:52 a.m., but were unable to determine a cause of death.

Several hours after her death, Klapper’s body was examined by a coroner’s investigator, who noticed that Klapper was missing an earring in her left ear, and the lycra pants she was wearing were on inside out. The investigator also noticed scratches on her face, including a half-moon scratch on her left cheek. The investigator examined the room at the Alistar Inn and in the trash can found a beer can, a carton of fuzzy navel mixed drink, and a styrofoam cup containing a yellowish liquid. None of the items had any odor except that of alcohol, and they were not preserved.

Dubria willingly spoke with Carlsbad police officers three times during the early morning of August 16, relating essentially the same story each time: he and Klapper had planned on staying at a campsite that night and when their plans to stay at the campsite fell through, they decided to get a motel room. They arrived at the Inn at about 11:30 p.m. He drank a beer and a mixed drink and Klapper had a few sips of the mixed drink. Klapper moved over on the bed she was lying on and signaled for Dubria to join her. He put his arm around her and they cuddled in the bed. They talked, kissed, and eventually had sex. He stated that, before they had intercourse, he asked her if she was using any birth control and she told him that she was taking birth control pills. After they had intercourse, Klapper went to the bathroom, then Dubria went to the bathroom, and they went to sleep in the same bed.

Dubria stated that, after Klapper fell asleep, she tossed and turned. At about 3:00 a.m., he awoke to go to the bathroom. While in the bathroom, he heard a “thud” and a moan and, when he returned, he found Klapper on the floor. She was not breathing and had no pulse. He administered CPR for about five minutes. He then panicked and, instead of calling 911 from the room, he ran out of the room for help. The person working in the motel office told him to call 911 from his room. *999 He ran back to the room, found himself locked out, ran back to the motel office, got a spare key, and ran back to the room to call 911. The police arrived a few minutes later. Dubria, who had been with Klapper almost continuously that day and night, stated that he had no idea why she died.

After Dubria returned to the medical facility where he was working in New Jersey, an autopsy was performed on Klap-per’s body. The examiner, forensic pathologist Dr. Leena Jariwala, found some cuts and abrasions on Klapper’s right eyelid, her right chin, her left cheek, and the tip of her nose. Dr. Jariwala concluded that these injuries were inflicted before Klap-per’s heart stopped beating. Dr. Jariwala and the emergency personnel also concluded that these injuries were inconsistent with the efforts of emergency personnel to revive her on the night of her death. Dr. Jariwala’s examination also revealed that Klapper had sexual intercourse relatively close to the time of her death. After completing the autopsy, Dr. Jariwala could find no cause of death.

Toxicological tests were performed and the only anomalous result was a heightened level of chloroform in Klapper’s blood, liver tissue, and gastric organs. Dr. Jariwala concluded that the cause of death was chloroform intoxication.

On October 23, 1991, Carlsbad detectives visited Dubria at his New Jersey home. They interviewed him at a nearby office. The officers told Dubria that they believed he had accidently murdered Klap-per when he administered chloroform in order to rape her. Dubria stuck to his story that he had no idea how Klapper had died and specifically denied trying to rape her or playing any role in her death. The officers did not arrest Dubria that day but later charged him with Klapper’s rape and murder.

At trial, Dr. Lucien Morris, a state expert with extensive knowledge of chloroform, explained that chloroform is an extremely potent and dangerous anesthetic. He stated that the standard method for administration of chloroform was to place one drop on a cloth over a patient’s face, return in one minute and place two drops on the cloth, then return in another minute and again double the dose and so on until the desired level of anesthesia is reached. This method avoids sudden exposure to concentrations of chloroform, which can be lethal. Chloroform is now seldom used because the margin of error between enough chloroform and too much is very small.

Dr. Morris noted that death from chloroform inhalation can occur when a small amount of chloroform is inhaled suddenly. The concentration of chloroform in the blood rises quickly and disrupts the heart. The amount of chloroform that can cause death under these circumstances is very small. Dr. Morris also noted the dangers of administering chloroform to a sleeping person. He explained that, if the person awakened and became frightened, the resulting release of adrenaline could interact adversely with the chloroform. Dr. Morris concluded that Klapper had died from a sudden inhalation of a small dose of chloroform.

Dr. Morris also stated that, although chloroform has a strong odor, the odor does not persist. “He testified, that assuming Dubria administered chloroform to Klapper in the motel room, it would have been possible for the smell to have dissipated before the police and emergency personnel arrived.

Dr. Gregory Schwartz, the defense medical expert and an emergency room physician, agreed with Dr. Morris about the dangers of chloroform. Dr. Schwartz concluded that Klapper died after having ingested, rather than inhaled, chloroform. He noted that chloroform’s use as a recreational drug is on the rise, although it is still relatively rare. He thought Klapper had overdosed on chloroform. He stated that, if she had inhaled chloroform, the odor would not have dissipated before the police and emergency room personnel arrived because the smell would persist in a *1000 closed room for eight to twelve hours. He noted that, if Klapper had ingested the chloroform, less vapor would have evaporated and there would be less of a smell. He conceded, however, that one could get rid of the smell of chloroform quickly. Dr. Schwartz also believed that the injuries to Klapper’s face were consistent with attempts to revive her.

Dubria took the stand in his own defense. He stated that his relationship with Klapper was not platonic. Before he and Klapper had gone to California, he had been on several formal dates with her. He had been attracted to her since early in their relationship and he had first kissed and cuddled with her in April 1991, and then again in May 1991 after going bowling. Dubria’s testimony about the night of Klapper’s death was consistent with the story that he had repeated to police immediately after Klapper’s death and at the later interview in New Jersey.

The jury convicted Dubria of first degree murder, rape by the use of drugs, and administering a drug in order to enable and assist himself to commit a felony. On the murder charge, the jury also found the special circumstance of rape to be true, and Dubria was sentenced to life in prison without the possibility of parole. Dubria appealed to the California Court of Appeal. His direct appeal and state habeas petition were consolidated and both were denied in a written unpublished opinion on July 18, 1995. His petition for review by the California Supreme Court was denied without opinion on October 19, 1995, and his petition for a writ of certiorari to the United State Supreme Court was denied on February 20, 1996, Dubria v. California, 516 U.S. 1118 , 116 S.Ct. 923 , 133 L.Ed.2d 852 (1996).

Dubria filed the instant habeas petition in federal district court, which denied the petition on the merits. He timely filed an appeal and a three-judge panel reversed the district court, see Dubria v. Smith, 197 F.3d 390 (9th Cir.1999). We granted the state’s petition for en banc review.

STANDARD OF REVIEW

We review the district court’s decision to grant or deny habeas relief de novo. See McNab v. Kok, 170 F.3d 1246, 1247 (9th Cir.1999) (per curiam). State court findings of fact are given a presumption of correctness. See 28 U.S.C. § 2254 (e)(1) (1996); Jeffries v. Wood, 114 F.3d 1484, 1499-1500 (9th Cir.1997) (en banc). The district court’s factual findings are reviewed for clear error. See Houston v. Roe, 177 F.3d 901, 905 (9th Cir.1999). Claims of ineffective assistance of counsel are mixed questions of law and fact and are reviewed de novo. See Crotts v. Smith, 73 F.3d 861, 864 (9th Cir.1996), superseded by statute as stated in Van Tran v. Lindsey, 212 F.3d 1143 (9th Cir.2000). 1

ANALYSIS

1. The Pre-Arrest Interview

Dubria claims constitutional error from the admission of the unredacted tape and transcript of his New Jersey interview by police detectives. During this interview, the detectives, in particular Detective Detar, challenged Dubria about his explanation of the events and repeatedly told him that no judge or jury would believe him if he stuck to his story. The state claims that Dubria procedurally defaulted on this issue by failing to make a contemporaneous objection at trial. The state also argues in the alternative that, even if there is no procedural bar, the district court did not commit error in admitting the unredacted tapes.

We conclude that we may examine the merits of this issue because defense counsel made a sufficiently broad objection at trial and because the state appears to have waived any procedural bar by failing to *1001 raise the issue in its response to the habe-as petition, see United States v. Barron, 172 F.3d 1153, 1156 (9th Cir.1999) (en banc). “Because there are no extraordinary circumstances present in this case which would suggest that justice would be served by overlooking the government’s omission,” id. at 1156-57 , we conclude that even if defense counsel’s objection was not adequate, the State waived its right to claim procedural default.

Reaching the merits of this claim, we conclude that Dubria cannot meet the standard that the admission of the tape and transcript “so fatally infected the proceedings as to render them fundamentally unfair.” Jammal v. Van de Kamp, 926 F.2d 918, 919 (9th Cir.1991). “ ‘[F]ederal habeas corpus relief does not lie for errors of state law.’” Estelle v. McGuire, 502 U.S. 62, 67 , 112 S.Ct. 475 , 116 L.Ed.2d 385 (1991) (quoting Lewis v. Jeffers, 497 U.S. 764, 780 , 110 S.Ct. 3092 , 111 L.Ed.2d 606 (1990)). Therefore, we cannot grant habeas relief upon reexamination of state-court determinations of questions of state law; we can grant relief only when the conviction “vielate[s] the Constitution, laws, or treaties of the United States.” Id. at 68, 112 S.Ct. 475 .

The question before us is whether admission of the unredacted tape and transcript violated Dubria’s constitutional right to due process. Dubria acknowledges that the tape and transcript were admissible for a limited purpose — to show that, when confronted with the toxicological tests, Dubria could not and did not explain why a woman he was continuously alone with for the prior 24 hours suddenly turned up dead from chloroform intoxication. When confronted with the toxicological tests, Dubria maintained that he was not involved in Klapper’s death. He also suggested that maybe Klapper took the chloroform herself or that both of them may have been exposed to chloroform when they drove behind a chemical truck.

Dubria claims instead that certain portions of the tape and transcript should have been redacted. He argues that Detective Detar’s comments and questions contained statements of disbelief of Dub-ria’s story, opinions concerning Dubria’s guilt, elaborations of the police theory of Klapper’s death, and references to Dub-ria’s involvement in the crime. Viewed in its entirety, however, the tape and transcript show what the state appellate courts quite properly described as an “unremarkable interview.” 2 The questions and comments by Detective Detar placed Dubria’s answers in context, much like a prosecutor’s questions at trial. There was nothing in Detective Detar’s statements that suggested evidence or theories of the case that were not presented at trial’

Nor do we find conclusive the argument that the jury impermissibly gave the comments added weight because they were made by a law enforcement officer. Although we have cautioned that testimony of law enforcement officers “ ‘often carries an aura of special reliability and trustworthiness,’ ” United States v. Gutierrez, 995 F.2d 169, 172 (9th Cir.1993) (quoting United States v. Espinosa, 827 F.2d 604, 613 (9th Cir.1987)), we examine officers’ statements in context to determine whether they fundamentally affect the fairness of the trial, see id. (no error in introduction of evidence). 3 Here, Detective De- *1002 tar’s statements were questions in a pretrial interview that gave context to Dub-ria’s answers. They were not the types of statements that carry any special aura of reliability. Cf. Gutierrez, 995 F.2d at 172 (district court did not abuse discretion in admitting officer’s testimony in court that defendant’s behavior was “furtive”); Espinosa, 827 F.2d at 612 (officer’s expert testimony in court that defendant acted in accordance with usual criminal modus op-erandi was admissible).

Furthermore, even if it was error to admit the tapes and transcripts without redacting Detective Detar’s statements, any error was cured by the judge’s two cautionary instructions. In response to an objection by defense counsel, the judge told the jury:

Later, the judge repeated to the jury:

Any impression that the jury may have had that it could consider Detective De-tar’s statements to be true was specifically and timely corrected by the trial judge. See Donnelly v. DeChristoforo, 416 U.S. 637, 644 , 94 S.Ct. 1868 , 40 L.Ed.2d 431 (1974). Ordinarily, a cautionary instruction is presumed to have cured prejudicial impact. See United States v. Merino-Balderrama, 146 F.3d 758, 764 (9th Cir.1998).

This is not a case in which the statements at issue are so clearly prejudicial that a curative instruction could not mitigate their effect. Dubria attempts to draw an analogy to Bruton v. United States, 391 U.S. 123 , 88 S.Ct. 1620 , 20 L.Ed.2d 476 (1968), in which the Supreme Court concluded that a curative instruction was insufficient to mitigate the prejudicial effect of a co-defendant’s confession that implicated the appellant. In that case, the Court held that the jury could not perform the overwhelming task of considering the confession in determining the guilt of the co-defendant and then ignoring it when determining the guilt of the appellant. 4 See id. at 131 , 88 S.Ct. 1620 . Here, in contrast, the jury had to simply do what it is asked to do all the time — consider the questions posed by Detective Detar as mere questions and not as evidence.

Further, the Court in Bruton based its holding in part on the fact that the co-defendant never testified at trial and, therefore, that the appellant was denied his constitutional right of confrontation. See id. at 128 , 88 S.Ct. 1620 . Here, there was no denial of that right, as both Detective Detar and Dubria took the stand and could be questioned about the interview.

Finally, while it is clear that, under California law, tapes should be redacted to remove material that is either impermissible or would unfairly prejudice the defense, see People v. Sanders, 75 Cal.App.3d 501, 508 , 142 Cal.Rptr. 227 (1977), *1003 “not every trial error or infirmity which might call for application of supervisory powers correspondingly constitutes a ‘failure to observe that fundamental fairness essential to the very concept of justice.’ ” Donnelly, 416 U.S. at 642 , 94 S.Ct. 1868 (quoting Lisenba v. California, 314 U.S. 219, 236 , 62 S.Ct. 280 , 86 L.Ed. 166 (1941)). We conclude that admission of these comments and statements did not violate Dub-ria’s fundamental right to due process.

2. Prosecutor’s Closing Argument/Ineffective Assistance of Counsel

While en banc review of this appeal was pending, the Supreme Court decided Slack v. McDaniel, — U.S. -,-, 120 S.Ct. 1595, 1600-01 , 146 L.Ed.2d 542 (2000). Slack held that AEDPA governs the right to appeal a district court’s dismissal of a habeas petition, like Dubria’s, pending on AEDPA’s effective date, April 24, 1996. Id.

AEDPA amended 28 U.S.C. § 2253 , which now provides, in pertinent part, that “[ujnless a circuit justice or judge issues a certificate of appealability, an appeal may not be taken to the court of appeals.... The certificate of appealability ... shall indicate which specific issue or issues satisfy the showing requirement.” Slack held that the court of appeals should have treated the petitioner’s notice of appeal as an application for a certificate of appealability (“COA”). It then examined the issues to determine if any met the showing requirement. See id. at 1603 . If Dubria had not filed a motion for a COA in the district court, we could treat his notice of appeal as a motion for a COA and Slack would not change our ability to consider any issue we concluded met the showing requirement. See Schell v. Witek, 218 F.3d 1017 at n. 4 (9th Cir.2000) (en banc). Dubria, however, did file a motion for a COA in the district court and the district court explicitly refused to certify for appeal the issue of trial counsel’s failure to object to statements made by the prosecutor in closing argument that Dubria was a liar, that he made up a story, and that the story was “garbage.” 5

The original panel, ruling without the benefit of Slack , followed our precedent, and that of seven other circuits, and held that the district court improperly applied the COA procedure because Dubria’s petition was filed prior to AEDPA’s effective date. The panel concluded that it was not limited by the COA and could address all issues on appeal. The panel relied in part on defense counsel’s failure to object to the “garbage” statement made by the prosecutor to conclude that defense counsel provided ineffective assistance.

Considering this issue on the merits, however, we conclude that defense counsel did not provide ineffective assistance. Dubria’s claim arises out of trial counsel’s failure to object to the following portion of the prosecutor’s closing argument:

To establish ineffective assistance of counsel, Dubria would have to show that his trial counsel’s failure to object to these statements fell outside the wide range of professionally competent assistance and that this deficient performance prejudiced his defense. See Strickland v. Washing *1004 ton, 466 U.S. 668, 687 , 104 S.Ct. 2052 , 80 L.Ed.2d 674 (1984).

Both the California Court of Appeal and the district court found that the “piece of garbage” reference, when read in context, referred to Dubria’s story, not to Dubria himself. We see no reason to disagree. Cf. Williams v. Borg, 139 F.3d 737, 744-45 (9th Cir.1998) (prosecutor’s reference to defense argument as “trash” not improper). Furthermore, even assuming that “piece of garbage” referred to Dubria, we would not conclude that trial counsel fell below the Strickland standard by not objecting. Cf. United States v. Laurins, 857 F.2d 529, 539 (9th Cir.1988) (statement that defendant was a liar could be construed as a comment on the evidence). While it is clear that prosecutors cannot express their opinion about a defendant’s guilt or vouch for government witnesses, see United States v. Molina, 934 F.2d 1440, 1444 (9th Cir.1991), a prosecutor is free to voice doubt about the veracity of a defendant’s story. See United States v. Sarno, 73 F.3d 1470, 1496-97 (9th Cir.1995); Molina, 934 F.2d at 1445 (the inference that one side is lying is unavoidable).

Dubria also claims that the last four lines of this portion of the prosecutor’s closing argument improperly suggested to the jury that the prosecutor had personal knowledge of Dubria’s character and guilt. 6 The prosecutor called Dubria a liar. He then stated that Dubria was “much worse than that. I’m not going to tell you. You can imagine some of the things I would tell you ... I’m not going to tell you, because you know.” The meaning of these words is unclear. These lines could refer to Dubria as a murderer and a rapist — what the prosecutor was trying to prove at trial. Given the ambiguity in these words, we conclude that a reasonably competent attorney could have refrained from objecting.

3. Remaining Claims

We have also considered Dubria’s other claims of violation of Miranda, instructional error, ineffective assistance of counsel, insufficiency of the evidence, exclusion of evidence of Mapper's knowledge of birth control methods, and unconstitutionality of his sentence, and hold that they are without merit.

AFFIRMED.

. Dubria filed his petition before the effective date of the Antiterrorism and Effective Death Penalty Act ("AEDPA”). Therefore, AEDPA's changes to our standard of review do not apply here. See Lindh v. Murphy, 521 U.S. 320 , 117 S.Ct. 2059 , 138 L.Ed.2d 481 (1997).

. The California Court of Appeal concluded that it found the interview

. We do not assume that the opinions of an investigating officer are presumptively prejudicial. Cf. United States v. Harber, 53 F.3d 236, 238, 240-41 (9th Cir.1995) (presuming *1002 prejudice when law enforcement officer’s report, introduced into evidence only for identification and to refresh officer’s memory as to certain facts, which included statements that officer thought defendant was guilty, was mistakenly given to the jury for their deliberations and was read by them).

. The facts of Bruton were even more compelling, in fact, because the co-defendant’s conviction was reversed on the ground that his confessions were inadmissible against him, and on retrial he was acquitted. See id. at 133 n. 9, 88 S.Ct. 1620 .

. Circuit Rule 22-1, effective January 1, 1999, requires that a petitioner file a motion in the court of appeals to expand a COA where the district court partially granted (he COA. The parties neither briefed nor argued on appeal before the original panel or before the en banc court whether Circuit Rule 22-1 precludes review of the “garbage” issue, see United States v. Zuno-Arce, 209 F.3d 1095, 1099-1100 (9th Cir.2000), and we decline to reach the issue here.

. The district court certified this issue for appeal.