Investigations require that detectives interpret what evidence tells them about the probability that a suspect committed a crime. Unfortunately, a large body of research suggests that people are generally unable to accurately assess what a specific element of information tells them about the likelihood of an outcome. Bayes’ Theorem, how- ever, can be used to overcome this difficulty. This article explores the use of Bayes’ Theorem to assess the question, “What does evidence tell us about the probability that someone is guilty?” A variety of analyses are presented, the results of which are not always intuitive. Policy implications are discussed.