An alibi is a defense that an accused person can use to prove that they were not present at the time and place of a crime. An alibi may be established through physical evidence, witness testimony, or a combination of both. There are two main types of alibis: direct alibi and circumstantial alibi. A direct alibi is when a witness or other person can testify that the accused was in fact somewhere else at the time of the crime, and could not have committed it. This alibi must be corroborated by other witnesses or physical evidence. A circumstantial alibi is when a witness or other person can testify that the accused was in fact somewhere else at the time of the crime, but there is no evidence to prove they could not have committed the crime. This alibi relies on circumstantial evidence to prove that the accused was not in the vicinity of the crime scene, but it is not as strong as a direct alibi.