The study was conducted by the Research Unit of the British Home Office. It aimed at examining the operation of the Judges' Rules and Administrative Directions, which regulate the handling of suspects, and at assessing the contribution of questioning to the detection of crime. During 3 months in 1979, a team made two 6-day visits to each of four police stations in town centers. The observers provided 24-hour coverage and concentrated on criminal cases. They were present during 220 police interviews and recorded data on standard forms. The findings suggest that the guidelines governing police interrogation are in most cases adequate to ensure that the courts may rely on the evidence which was gathered through suspects' responses. However, technical breaches of the guidelines did occur, and these raised questions about the proper balance between the needs of criminal investigation and the rights of suspects. Individual chapters focus on a history of the legal basis of the suspect's right to silence, the arrival at the police station and the time spent there, contact with persons other than police officers, the caution and the right to silence, interviews with suspects, the contribution of questioning to the detection of crime, the formal disposal of suspects, and a summary of the findings with conclusions. Appendixes contain the observer recording document and information on the nature of evidence against suspects for selected categories of crime. Data tables and a list of 16 references are included.