Gregoire, who left office this week, pardoned or reduced the sentences of 10 inmates, including Johnny Ray Stewart, 44, who is serving a life term, The Seattle Times reported Thursday.
Stewart alerted officials at the Washington State Penitentiary in Walla Walla in December 2001 that his cellmate, Steven Sherer, planned to have another inmate kill Marilyn Brenneman, who was senior deputy prosecutor at the time. Sherer was serving a 60-year sentence for killing his wife.
Police planted a listening device in the cell Stewart and Sherer shared, and recorded Sherer talking about the plan to kill Brenneman and to burn down the home of Sherer's former mother-in-law.
Authorities convinced a local newspaper to run a story that tricked Sherer into believing his intended accomplice had acted on the plan, and Sherer was eventually convicted of first-degree solicitation to commit arson and was sentenced to life in prison under Washington's three-strikes law.
Pierce County Prosecutor Mark Lindquist said Wednesday Gregoire's decision was based on Stewart coming forward with potentially lifesaving information.
"Whether one agrees or not, one could certainly understand why the governor would give it that weight," said Lindquist.
Stewart is serving a life term under the state's "three strikes" law for first-degree burglary and attempted robbery in King County. The other strikes are for second-degree assault in King County and first-degree manslaughter in Pierce County.
Gregoire's order calls for Stewart to agree to numerous conditions, and for a psychologist to determine his release would pose a low risk to the public, before he can be set free, the Times said.