Reasons for the high numbers of people with mental illness who are involved in the criminal justice system are complex and interrelated. While some suggest that the problem is the direct result of deinstitutionalization, the research does not support this simplistic explanation. There is no doubt that the shift away from institutional mental health care, and the associated underfunding of community-based mental health services, is at the heart of the problem, but there is little evidence that those formerly housed in institutions have been shifted to jails and prisons
Other sources of the problem include the lack of affordable housing, discrimination based on stereotypes associating mental illness with violence, crackdowns on public nuisance crimes, and tough prosecution of drug offenses. These forces, together with the inability of the criminal justice and mental health systems to recognize and address the problem, all contribute to this disturbing trend.