Destruction of evidence is the loss, complete destruction, or spoilage of material that could provide evidence in a case. There is a duty to preserve evidence for all parties to a case, and destruction is often viewed prejudicially, as the court assumes that the only reason to destroy evidence is a belief that it could be incriminating or exculpatory, depending on which party destroys it. There may be legal penalties for destruction of evidence.
Evidence can be destroyed in a variety of situations. Sometimes a party with custody of the evidence behaves negligently and loses it or exposes it to risks. For example, a medical examiner may fail to collect DNA evidence properly, making it impossible to test later. Likewise, a police officer might fail to observe chain of evidence procedures by leaving evidence unsecured on the seat of his vehicle, leading to loss of the evidence through theft.
In other cases, destruction of evidence may appear willful. Shredding documents is an example, as are attempts to deliberately ruin evidence like burning it or hiding it. This wanton destruction of evidence tends to be regarded with extreme suspicion. The court may rule in favor of the opposing party if the destruction of evidence comes to light, arguing that it might have played a critical role in the case and now cannot be used because of the destruction.
It is important to be aware that destruction of evidence is not always viewed negatively by the court. Sometimes it is necessary to subject evidence to destructive testing in order to uncover more information. Ideally both parties consent to this, and a judge rules that the testing should proceed. An example is DNA evidence; if there is only a small sample, the testing will ruin it and make it impossible to repeat it at another facility or in the future. Evidence analysts may be forced to make a decision between destroying evidence to collect vital information, or saving it and not being able to draw conclusions from testing.
Evidence is also destroyed routinely after a set period of time in closed cases. Once a court hears a matter and reaches a decision, the evidence is retained long enough to make it available for appeals, and then the party in charge of storing it has the right to destroy it. This frees up space for storage. Courts may decide to keep evidence with historical or legal interest beyond this mandatory holding period.