If a laboratory consumed the only physical sample during homicide testing, that fact alone does not require exclusion of the result or dismissal of a case. The next questions are what was known about the sample before it was used, whether the evidence was apparently exculpatory or only potentially useful, whether comparable evidence remains, and what records or data another expert can still review.

Federal due-process law draws an important distinction. Under California v. Trombetta, evidence must have had apparent exculpatory value before it was destroyed, and the defendant must be unable to obtain comparable evidence by reasonably available means. (California v. Trombetta, 467 U.S. 479 (1984)) If evidence was only potentially useful, Arizona v. Youngblood requires police bad faith; negligence or a failure to preserve, by itself, is not enough under that rule. (Arizona v. Youngblood, 488 U.S. 51 (1988)) The facts and applicable procedures matter. A sample exhausted during a documented test, evidence lost or destroyed before testing, and a trace that was never collected are different situations.

Identify what was consumed and what remains

Start by tracing the evidence from collection through the reported result. Depending on the test, counsel or an expert may want to examine:

  • where and when the specimen was collected, and how it was packaged and transferred;
  • its condition and quantity before testing, the method selected, and why the lab used that method;
  • extraction, aliquot, and consumption records, including whether any extract, slide, swab, or other material remains;
  • controls, validation information relevant to the method, raw output, instrument data, analyst notes, and the final report.

Not every method creates every listed record or leaves a testable remainder. The point is to establish what this lab did and what information exists—not to assume that a second laboratory can recreate a sample that no longer exists. Even when physical retesting is impossible, another qualified expert may be able to assess the method and retained data, depending on what is available.

The timing and circumstances of loss matter

For a Trombetta claim, the question is whether the evidence’s exculpatory value was apparent before destruction and whether comparable evidence could reasonably be obtained. For evidence that was only potentially useful, Youngblood asks whether police acted in bad faith. A disappointing result, missing material, or careless handling does not automatically establish either test.

The review may consider what investigators and the lab knew before testing, whether the defense or a court had requested preservation, whether a protocol or order applied, and whether any comparable sample or underlying data remain. Those facts may inform a legal claim, but they do not predetermine a remedy.

California’s discovery statute separately requires the prosecution to disclose specified material, including relevant evidence obtained in the investigation and exculpatory evidence, when it is in the prosecutor’s possession or known to be in the investigating agencies’ possession. It also addresses the specified expert statements and test results the prosecution intends to offer at trial. (Penal Code § 1054.1) A request for broader raw data, lab access, or a particular remedy requires case-specific analysis; the statute should not be read as guaranteeing every underlying file or an independent retest.

A lawyer and, where appropriate, an independent forensic expert can review the lab file, remaining materials, and preservation history before assessing available options. The Law Offices of David S. Chesley handles homicide defense in Los Angeles and can be reached at (800) 755-5174.