California v. Trombetta

Justice Marshall delivered the opinion of the Court.

The Due Process Clause of the Fourteenth Amendment requires the State to disclose to criminal defendants favorable evidence that is material either to guilt or to punishment. United States v. Agurs, 427 U. S. 97 (1976); Brady v. [*481] Maryland, 373 U. S. 83 (1963). This case raises the question whether the Fourteenth Amendment also demands that the State preserve potentially exculpatory evidence on behalf of defendants. In particular, the question presented is whether the Due Process Clause requires law enforcement agencies to preserve breath samples of suspected drunken drivers in order for the results of breath-analysis tests to be admissible in criminal prosecutions. f — I The Omicron Intoxilyzer (Intoxilyzer) is a device used in California to measure the concentration of alcohol in the blood of motorists suspected of driving while under the influence of intoxicating liquor.[1] The Intoxilyzer analyzes the suspect’s breath. To operate the device, law enforcement officers follow these procedures:

“Prior to any test, the device is purged by pumping clean air through it until readings of 0.00 are obtained. The breath test requires a sample of‘alveolar’ (deep lung) air; to assure that such a sample is obtained, the subject is required to blow air into the intoxilyzer at a constant pressure for a period of several seconds. A breath sample is captured in the intoxilyzer’s chamber and infrared light is used to sense the alcohol level. Two samples are taken, and the result of each is indicated on a printout card. The two tests must register within 0.02 of each other in order to be admissible in court. After each test, the chamber is purged with clean air and then [*482] checked for a reading of zero alcohol. The machine is calibrated weekly, and the calibration results, as well as a portion of the calibration samples, are available to the defendant.” 142 Cal. App. 3d 138, 141-142, 190 Cal. Rptr. 319, 321 (1983) (citations omitted).