In theory, the prosecution service decides which offenders should be diverted from prosecution, but in practice, selection is largely determined by the police. The police report plays the crucial role in starting the diversion practice and prosecutors generally respond neutrally to the cues provided by the police. Consequently, any systematic bias is not caused by prosecutorial decision making but is imported at an earlier stage in the process. The key to expanding diversion from prosecution into psychiatric care is to require the police to provide more information. The article focuses upon the way in which justice system officials learn or deduce that an alleged offender might be mentally disturbed and come to consider an offer of psychiatric treatment as an alternative to prosecution. Given the critical role of the police in the selection of divertees for psychiatric treatment rather than prosecution, police training, working practices and culture are as key to the diversion process as the availability of resources. Notes, tables, references