Evidence, in broad terms, is anything that can support the truth of a statement. In law, evidence is anything that can support a legal claim or, on the other hand, show that a legal claim is false. Evidence tampering is an illegal action in which evidence is either falsified, edited, or amended in order to support or undermine a legal claim.
Let's say, for example, that a person was being sued for refusing to pay a bill. If the person being sued altered the related invoice, statement, or bank records to make it seem as if he had paid the bill, that would be a clear case of evidence tampering. This is illegal and is punishable by law. Those who are convicted of this crime can be forced to pay fines and even serve time in jail or prison.
While documents can be tampered with, evidence tampering can also involve physical evidence. When police are investigating a crime scene, it is important that the space is secured and that no one alters the scene until professionals can examine everything. Removing or even repositioning anything within a crime scene is evidence tampering. In fact, placing new items within a crime scene is also tampering with evidence.
One of the main reasons that people tamper with evidence is to change the perception of past events. The 2002 film Insomnia starring Al Pacino, Hilary Swank, and Robin Williams is a film largely based on evidence tampering. In the movie, Al Pacino's character is a police officer named Will Dormer who is guilty of planting evidence. In the film, Will Dormer accidentally shoots and kills a colleague while pursuing a suspect in a murder case. While trying to bring the murderer to justice, he also plants evidence against him in an attempt to reassign blame for his colleague's death.
It is not always possible to figure out whether or not evidence has been tampered with. This is especially true if evidence has been destroyed. If documents which can be used as evidence have been shredded or burned, for example, it can be very difficult to restore them enough to decipher their original text. It is also not always possible to tell if a piece of evidence has been falsified. Evidence tampering can seriously change the course of legal decisions and proceedings and can even lead to punishments for innocent parties or gains for guilty parties.