What is the legal test for destroying or destroying evidence in a criminal case?

As a matter of due process, law enforcement agencies have a duty to preserve evidence that might be expected to play a significant role in the suspect's defense. Such "evidence must both possess an exculpatory value that was apparent before the evidence was destroyed, and be of such a nature that the defendant would be unable to obtain comparable evidence by other reasonably available means." (California v. Trombetta (1984) 467 U.S. 479, 488-489 [104 S.Ct. 2528].) If all that a defendant can say about the unpreserved evidence is that it could have been tested and the results might have helped the defense, the defendant must show that the police acted in bad faith in losing or disposing of the material. (Arizona v. Youngblood (1988) 488 U.S. 51, 57-58 [109 S.Ct. 333]; People v. DePriest (2007) 42 Cal.4th 1, 42.) "The presence or absence of bad faith by the police . . . must necessarily turn on the police's knowledge of the exculpatory value of the evidence at the time it was lost or destroyed." (Youngblood, at p. 56, fn. *.) Negligent destruction of, or failure to preserve, potentially exculpatory evidence, without evidence of bad faith, does not violate due process. (Id. at p. 58.)