The faulty risk-assessment program predicted the offenders could be released under the state's non-revocable parole law that took effect in January 2010. It was part of a statewide effort intended to reduce prison crowding and cost.
The inspector general found that about 1,500 offenders were improperly left unsupervised, including 450 who "carry a high risk for violence." The offenders otherwise would have been released under traditional parole, which requires them to report in regularly and follow specific rules.
The new law was designed for less serious offenders. Under non-revocable parole, offenders don't report to parole agents and can't be sent back to prison unless they commit new crimes.
The Department of Corrections and Rehabilitation said it relies heavily on a computerized program because it must review the criminal histories of more than 160,000 inmates and more than 100,000 offenders on parole.
Auditors found the risk assessment was wrong for 23.5 percent of more than 10,000 offenders who were considered for non-revocable parole between January and July 2010. Some were scored too high and others too low, with the lower-scoring inmates eligible for unsupervised release.
Even after the computer program was altered, analysts determined it was wrong in 8 percent of cases.
The department disputed the inspector general's analysis and conclusion.
"Alleged `errors' ... have in large part been corrected," Lee Seale, the department's deputy chief of staff, wrote in a rebuttal letter. "We reject the notion that the California Static Risk Assessment is flawed and dispute the evidence (cited) in support of this claim."
The version of the assessment reviewed by the inspector general has now been obsolete for over a year, Seale wrote, and the department will keep working to improve the program developed by the University of California, Irvine, Center of Evidence-based Corrections.
Seale said the program has saved money and cut prison overcrowding by keeping many parole violators from returning to prison - important developments given current events.
The report came as the state struggles to safely release less dangerous convicts and parolees to help combat a $10 billion budget deficit. Compounding the pressure, the U.S. Supreme Court ruled Monday that the state must reduce its prison population by about 33,000 inmates over the next two years to reduce crowding and improve care for mentally and physically ill inmates.