Many people who witness crimes become suspects. Many people who commit crimes invent perpetrators who do not exist. How can you evaluate the probability that a witness could be lying and potentially be the perpetrator? I will give two examples, one is a specific case.
Witness identifies a vague description of a single person of a racial/ethnic minority that frequently commits crimes in the area of the act in question.
In the case of Dr. Jeffery R. MacDonald, he identified four people, each with different racial characteristics, and included details about hair and articles of clothing. The description also included that they were drug users, and the nature of the crime suggested they also are involved with satan worship. The description of a woman was so specific that it lead to a unique person. In addition to what I imagine is a low probability of Jeffery R. MacDonald imagining a real person that exists (in the case that he is the perpetrator, not the witness), what is the probability of the details of this person's confession matching the details of the crime if they did not commit the crime, and then for each additional witness statement corroborating the vehicles she was in, who she was with, time she answered the phone, etc?