A two-phased experiment tested the hypothesis that the presumption of guilt that underlies police interrogations activates a process of behavioral confirmation. In Phase I, 52 suspects guilty or innocent of a mock theft were questioned by 52 interrogators led to believe that most suspects were guilty or innocent. Interrogators armed with guilty as opposed to innocent expectations selected more guilt-presumptive questions, used more interrogation techniques, judged the suspect to be guilty, and exerted more pressure to get a confession-particularly when paired with innocent suspects. In Phase II, neutral observers listened to audiotapes of the suspect, interrogator, or both. They perceived suspects in the guilty expectations condition as more defensive-and as somewhat more guilty. Results indicate that a presumption of guilt sets in motion a process of behavioral confirmation by which expectations influence the interrogator's behavior, the suspect's behavior, and ultimately the judgments of neutral observers.