The guidelines for evidence collection refer to the legal rules of a jurisdiction that dictate how law enforcement officials may collect evidence to prove the commission of a crime or the commission of a tort. Evidence can constitute anything used to demonstrate an accused individual's guilt in criminal activity or in a civil case. Different rules apply for evidence collection in criminal versus civil trials within the United States, as well as in many other countries.
In a criminal case, evidence is anything that proves one of the elements of a crime. Evidence in a criminal case may be the gun used in a killing, a vehicle with a spot of blood in it, DNA evidence, or a bag of drugs taken from an accused drug dealer's home. It can also be something that alone seems innocent, such as an ATM receipt, but which proves intent, motive, or some other aspect of a crime the prosecutor must prove.
Within the United States, the rules for evidence collection in a criminal case are set forth in the Fourth Amendment, which protects against unreasonable search and seizure. The Fourth Amendment states "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
This means that, when collecting evidence, law enforcement must obtain a warrant from a judge after demonstrating probable cause. Other evidence rules may also apply that limit evidence collection. For example, rules within the United States dictate that anything found, even indirectly, as the result of an unlawful search or confession is excluded from being heard in court, as it is "fruit of the tainted tree."
In a civil case, the evidence collection rules are set by rules relating to discovery. Discovery is the process by which the plaintiff and defendant exchange information necessary to either prove the case or defend against the accusations. The rules for discovery generally stipulate that requests for documents must be reasonable; for example, in an attempt to prove wrongful termination, an individual could reasonably request that the defendant turn over her performance reviews for the past ten years, but the individual could not request that the company turn over every performance review written for every single employee in the 100-year history of the company, as such a request would be unreasonable.