delivered the opinion of the Court.
Respondent Larry Youngblood was convicted by a Pima County, Arizona, jury of child molestation, sexual assault, and kidnaping. The Arizona Court of Appeals reversed his conviction on the ground that the State had failed to preserve semen samples from the victim’s body and clothing. 153 Ariz. 50, 734 P. 2d 592 (1986). We granted certiorari to consider the extent to which the Due Process Clause of the Fourteenth Amendment requires the State to preserve evidentiary material that might be useful to a criminal defendant.
On October 29, 1983, David L., a 10-year-old boy, attended a church service with his mother. After he left the service at about 9:30 p.m., the boy went to a carnival behind the church, where he was abducted by a middle-aged man of medium height and weight. The assailant drove the boy to a secluded area near a ravine and molested him. He then took the boy to an unidentified, sparsely furnished house where he sodomized the boy four times.. Afterwards, the assailant tied the boy up while he went outside to start his car. Once the assailant started the car, albeit with some difficulty, he returned to the house and again sodomized the boy. The assailant then sent the boy to the bathroom to wash up before he returned him to the carnival. He threatened to kill the boy if he told anyone about the attack. The entire ordeal lasted about YA hours.
After the boy made his way home, his mother took him to Kino Hospital. At the hospital, a physician treated the boy for rectal injuries. The physician also used a “sexual assault kit” to collect evidence of the attack. The Tucson Police De*53partment provided such kits to all hospitals in Pima County for use in sexual assault cases. Under standard procedure, the victim of a sexual assault was taken to a hospital, where a physician used the kit to collect evidence. The kit included paper to collect saliva samples, a tube for obtaining a blood sample, microscopic slides for making smears, a set of Q-Tip-like swabs, and a medical examination report. Here, the physician used the swab to collect samples from the boy’s rectum and mouth. He then made a microscopic slide of the samples. The doctor also obtained samples of the boy’s saliva, blood, and hair. The physician did not examine the samples at any time. The police placed the kit in a secure refrigerator at the police station. At the hospital, the police also collected the boy’s underwear and T-shirt. This clothing was not refrigerated or frozen.
Nine days after the attack, on November 7, 1983, the police asked the boy to pick out his assailant from a photographic lineup. The boy identified respondent as the assailant. Respondent was not located by the police until four weeks later; he was arrested on December 9, 1983.
On November 8, 1983, Edward Heller, a police criminologist, examined the sexual assault kit. He testified that he followed standard department procedure, which was to examine the slides and determine whether sexual contact had occurred. After he determined that such contact had occurred, the criminologist did not perform any other tests, although he placed the assault kit back in the refrigerator. He testified that tests to identify blood group substances were not routinely conducted during the initial examination of an assault kit and in only about half of all cases in any event. He did not test the clothing at this time.
Respondent was indicted on charges of child molestation, sexual assault, and kidnaping. The State moved to compel respondent to provide blood and saliva samples for comparison with the material gathered through the use of the sexual assault kit, but the trial court denied the motion on the *54ground that the State had not obtained a sufficiently large semen sample to make a valid comparison. The prosecutor then asked the State’s criminologist to perform an ABO blood group test on the rectal swab sample in an attempt to ascertain the blood type of the boy’s assailant. This test failed to detect any blood group substances in the sample.
In January 1985, the police criminologist examined the boy’s clothing for the first time. He found one semen stain on the boy’s underwear and another on the rear of his T-shirt. The criminologist tried to obtain blood group substances from both stains using the ABO technique, but was unsuccessful. He also performed a P-30 protein molecule test on the stains, which indicated that only a small quantity of semen was present on the clothing; it was inconclusive as to the assailant’s identity. The Tucson Police Department had just begun using this test, which was then used in slightly more than half of the crime laboratories in the country.
Respondent’s principal defense at trial was that the boy had erred in identifying him as the perpetrator of the crime. In this connection, both a criminologist for the State and an expert witness for respondent testified as to what might have been shown by tests performed on the samples shortly after they were gathered, or by later tests performed on the samples from the boy’s clothing had the clothing been properly refrigerated. The court instructed the jury that if they found the State had destroyed or lost evidence, they might “infer that the true fact is against the State’s interest.” 10 Tr. 90.
The jury found respondent guilty as charged, but the Arizona Court of Appeals reversed the judgment of conviction. It stated that “‘when identity is an issue at trial and the police permit the destruction of evidence that could eliminate the defendant as the perpetrator, such loss is material to the defense and is a denial of due process.’” 153 Ariz., at 54, 734 P. 2d, at 596, quoting State v. Escalante, 153 Ariz. 55, 61, 734 P. 2d 597, 603 (App. 1986). The Court of Ap*55peals concluded on the basis of the expert testimony at trial that timely performance of tests with properly preserved semen samples could have produced results that might have completely exonerated respondent. The Court of Appeals reached this conclusion even though it did “not imply any bad faith on the part of the State.” 153 Ariz., at 54, 734 P. 2d, at 596. The Supreme Court of Arizona denied the State’s petition for review, and we granted certiorari. 485 U. S. 903 (1988). We now reverse.
Decision of this case requires us to again consider “what might loosely be called the area of constitutionally guaranteed access to evidence.” United States v. Valenzuela-Bernal, 458 U. S. 858, 867 (1982). In Brady v. Maryland, 373 U. S. 83 (1963), we held that “the suppression by the prosecution of evidence favorable to the accused upon request violates due process where the evidence is material either to guilt or to punishment, irrespective of the good faith or bad faith of the prosecution.” Id., at 87. In United States v. Agurs, 427 U. S. 97 (1976), we held that the prosecution had a duty to disclose some evidence of this description even though no requests were made for it, but at the same time we rejected the notion that a “prosecutor has a constitutional duty routinely to deliver his entire file to defense counsel.” Id., at 111; see also Moore v. Illinois, 408 U. S. 786, 795 (1972) (“We know of no constitutional requirement that the prosecution make a complete and detailed accounting to the defense of all police investigatory work on a case”).
There is no question but that the State complied with Brady and Agurs here. The State disclosed relevant police reports to respondent, which contained information about the existence of the swab and the clothing, and the boy’s examination at the hospital. The State provided respondent’s expert with the laboratory reports and notes prepared by the police criminologist, and respondent’s expert had access to the swab and to the clothing.
*56If respondent is to prevail on federal constitutional grounds, then, it must be because of some constitutional duty over and above that imposed by cases such as Brady and Agurs. Our most recent decision in this area of the law, California v. Trombetta, 467 U. S. 479 (1984), arose out of a drunken driving prosecution in which the State had introduced test results indicating the concentration of alcohol in the blood of two motorists. The defendants sought to suppress the test results on the ground that the State had failed to preserve the breath samples used in the test. We rejected this argument for several reasons: first, “the officers here were acting in ‘good faith and in accord with their normal practice,’” id., at 488, quoting Killian v. United States, 368 U. S. 231, 242 (1961); second, in the light of the procedures actually used the chances that preserved samples would have exculpated the defendants were slim, 467 U. S., at 489; and, third, even if the samples might have shown inaccuracy in the tests, the defendants had “alternative means of demonstrating their innocence.” Id., at 490. In the present case, the likelihood that the preserved materials would have enabled the defendant to exonerate himself appears to be greater than it was in Trombetta, but here, unlike in Trombetta, the State did not attempt to make any use of the materials in its own case in chief. *
*57Our decisions in related areas have stressed the importance for constitutional purposes of good or bad faith on the part of the Government when the claim is based on loss of evidence attributable to the Government. In United States v. Marion, 404 U. S. 307 (1971), we said that “[n]o actual prejudice to the conduct of the defense is alleged or proved, and there is no showing that the Government intentionally delayed to gain some tactical advantage over appellees or to harass them.” Id., at 325; see also United States v. Lovasco, 431 U. S. 783, 790 (1977). Similarly, in United States v. Valenzuela-Bemal, supra, we considered whether the Government’s deportation of two witnesses who were illegal aliens violated due process. We held that the prompt deportation of the witnesses was justified “upon the Executive’s good-faith determination that they possess no evidence favorable to the defendant in a criminal prosecution.” Id., at 872.
The Due Process Clause of the Fourteenth Amendment, as interpreted in Brady, makes the good or bad faith of the State irrelevant when the State fails to disclose to the defendant material exculpatory evidence. But we think the Due Process Clause requires a different result when we deal with the failure of the State to preserve evidentiary material of which no more can be said than that it could have been subjected to tests, the results of which might have exonerated the defendant. Part of the reason for the difference in treatment is found in the observation made by the Court in Trombetta, supra, at 486, that “[w]henever potentially excul*58patory evidence is permanently lost, courts face the treacherous task of divining the import of materials whose contents are unknown and, very often, disputed.” Part of it stems from our unwillingness to read the “fundamental fairness” requirement of the Due Process Clause, see Lisenba v. California, 314 U. S. 219, 236 (1941), as imposing on the police an undifferentiated and absolute duty to retain and to preserve all material that might be of conceivable evidentiary significance in a particular prosecution. We think that requiring a defendant to show bad faith on the part of the police both limits the extent of the police’s obligation to preserve evidence to reasonable bounds and confines it to that class of cases where the interests of justice most clearly require it, i. e., those cases in which the police themselves by their conduct indicate that the evidence could form a basis for exonerating the defendant. We therefore hold that unless a criminal defendant can show bad faith on-the part of the police, failure to preserve potentially useful evidence does not constitute a denial of due process of law.
In this case, the police collected the rectal swab and clothing on the night of the crime; respondent was not taken into custody until six weeks later. The failure of the police to refrigerate the clothing and to perform tests on the semen samples can at worst be described as negligent. None of this information was concealed from respondent at trial, and the evidence — such as it was — was made available to respondent’s expert who declined to perform any tests on the samples. The Arizona Court of Appeals noted in its opinion— and we agree — that there was no suggestion of bad faith on the part of the police. It follows, therefore, from what we have said, that there was no violation of the Due Process Clause.
The Arizona Court of Appeals also referred somewhat obliquely to the State’s “inability to quantitatively test” certain semen samples with the newer P-30 test. 153 Ariz., at 54, 734 P. 2d, at 596. If the court meant by this statement *59that the Due Process Clause is violated when the police fail to use a particular investigatory tool, we strongly disagree. The situation here is no different than a prosecution for drunken driving that rests on police observation alone; the defendant is free to argue to the finder of fact that a breathalyzer test might have been exculpatory, but the police do not have a constitutional duty to perform any particular tests.
The judgment of the Arizona Court of Appeals is reversed, and the case is remanded for further proceedings not inconsistent with this opinion.
Reversed.
In this case, the Arizona Court of Appeals relied on its earlier decision in State v. Escalante, 153 Ariz. 55, 734 P. 2d 597 (1986), holding that ‘“when identity is an issue at trial and the police permit destruction of evidence that could eliminate a defendant as the perpetrator, such loss is material to the defense and is a denial of due process.’ ” 153 Ariz. 50, 54, 734 P. 2d 592, 596 (1986), quoting Escalante, supra, at 61, 734 P. 2d, at 603 (emphasis added). The reasoning in Escalante and the instant case mark a sharp departure from Trombetta in two respects. First, Trombetta speaks of evidence whose exculpatory value is “apparent.” 467 U. S., at 489. The possibility that the semen samples could have exculpated respondent if preserved or tested is not enough to satisfy the standard of constitutional materiality in Trombetta. Second, we made clear in Trombetta that the exculpatory value of the evidence must be apparent *57“before the evidence was destroyed.” Ibid, (emphasis added). Here, respondent has not shown that the police knew the semen samples would have exculpated him when they failed to perform certain tests or to refrigerate the boy’s clothing; this evidence was simply an avenue of investigation that might have led in any number of directions. The presence or absence of bad faith by the police for purposes of the Due Process Clause must necessarily turn on the police’s knowledge of the exculpatory value of the evidence at the time it was lost or destroyed. Cf. Napue v. Illinois, 360 U. S. 264, 269 (1959).