Evidence is defined as any material item or assertion that is submitted to the court in order to demonstrate the truth of an allegation or question of fact. Evidence is the backbone of the legal system and the cornerstone of any conviction.

When it comes to a criminal investigation there are two general types of evidence: physical evidence and testimonial evidence. Physical evidence is collected, usually by the police, and then preserved for use during the trial. Testimonial evidence is collected from key witnesses through the use of depositions.

Direct evidence is an item that speaks for itself. Examples of direct evidence include eyewitness accounts, confessions, or other evidence that does not need elaboration to prove a fact. Circumstantial evidence is the opposite. Circumstantial evidence implies a fact or inference through implying things. Both circumstantial and direct evidence are used in order to demonstrate either guilt or innocence.

Before something can be approved for admission into court, a proper chain of custody needs to be established. Any evidence that does not have an established chain of custody demonstrating that it has not been improperly tampered with will not be admissible in court.

What evidence is admissible varies from case to case. Attorneys for both sides will argue over what pieces of evidence should be admissible and why. Examples of evidence that may be declared inadmissible include expert witness testimony sections, scientific studies, or pieces of evidence that may be too prejudicial to be allowed in front of a jury.