Since a criminal case involves very high stakes, a defendant has a right to a fair trial under the Sixth Amendment to the Constitution. Among other things, this right requires the prosecution to preserve certain evidence obtained during its investigation of the case. During a process known as discovery, it must provide the defendant with the evidence that it will use in presenting its case. The prosecution also must provide the defendant with exculpatory evidence that could support a defense. This is because the prosecutor’s duty is to obtain justice rather than simply obtaining a conviction.
The evidence that must be preserved is limited to evidence that would be both material and exculpatory. Evidence is material if it is relevant to an important issue in the case, and evidence is exculpatory if it supports a defense or tends to show that the defendant is not guilty of the crime.
One of the most common types of exculpatory evidence is evidence that supports an alibi. This could consist of any statements or materials that suggest that the defendant was not in the location where the crime was committed at the time that it was committed or otherwise could not have committed the crime.
Other types of exculpatory evidence might consist of recorded statements of the defendant or witnesses, as well as recordings of 911 calls. It also might involve photographs, blood samples, and other tangible evidence from the scene of the crime. In some cases, law enforcement may need to preserve notes of their investigation, but this duty may extend only to notes that record an interrogation of the defendant.
A private person or entity does not have an obligation to preserve evidence, unless they were formally working for or with a law enforcement agency. (An example might be a scientific lab that is regularly retained by the prosecutor’s office to examine evidence.) However, most government agents have a responsibility to preserve evidence. These range from police and prosecutors to detectives and investigators working for the prosecutor’s office, administrative staff, and the Attorney General’s Office. The duty to preserve evidence starts as soon as the evidence is obtained and continues after a conviction to cover any exculpatory evidence that might assist a defendant in an appeal.
A court will not sanction the prosecution on its own if the prosecution loses or destroys evidence. A defendant or their attorney will need to raise the issue. They will need to show that the government acted in bad faith in violating the duty to preserve evidence, and they also need to show that the evidence was material and exculpatory, such that their right to a fair trial was violated. If the defendant succeeds, the court might suppress the related evidence or limit testimony about it. In some extreme cases, the court might even dismiss the case. If the issue does not arise until after a conviction, an appellate court might overturn the conviction and order a new trial.
Proving bad faith requires showing intentional misconduct by the government, rather than mere carelessness. A failure to follow procedures can suggest bad faith, but it is a challenging standard to meet.
Proving that the evidence was material requires showing that the government should have known that the evidence was exculpatory. The defense also needs to show that no other available evidence could have served the same purpose. If the prosecution usually preserves the evidence that was destroyed, or if it had planned to analyze this evidence, this suggests that it knew that the evidence was material.
