As many as 3,200 inmates may have been mistakenly released early from Washington state prisons since 2002 because of errors in calculating sentences, Governor Jay Inslee said on Tuesday.

Those inmates had been convicted of crimes including assault and robbery, and their convictions included "an enhancement" such as a firearm violation that should have extended their sentences, said Jeremy Barclay, a spokesman for the Washington Department of Corrections.

The sentencing enhancements are where the error occurred, Barclay said.

Inslee ordered the state Department of Corrections to temporarily halt all releases of prisoners with the enhanced sentences until a hand calculation ensured the offender would be set free correctly. State officials expect by the new year to have a fix for the software used to calculate release dates.

The problem follows a July 2002 state Supreme Court ruling that required the Department of Corrections to apply so-called "good time" credits earned in county jail to state prison sentences, Inslee said.

The department's programing fix to bring its sentencing into compliance with the ruling had an "inaccurate sequencing" that over-credited some offenders, Inslee said.

The 3,200 inmates released represent roughly 3 percent of all releases during the 13-year time period starting in 2002, Inslee said. Estimates indicate that the median number of days offenders were released from prison is 49 days before their correct release date.

State corrections authorities learned of the problem in 2012 but failed to fix it.

Inslee has retained an independent law firm to investigate the problem, which he called "maddening."

The majority of the offenders released early will be given "day for day" credit for their time in the community, Inslee said, though others will be tracked down and put on work release or hauled back to prison.