LANSING, Mich. -

A Michigan inmate who was poised to leave prison after more than 20 years is suing to force the state to honor a commutation order that was signed by a governor in 2010.

Matthew Makowski's life-without-parole sentence was commuted by Gov. Jennifer Granholm just days before she left office.

But she changed her mind after the victim's family protested.

Makowski admits planning the robbery of a co-worker in suburban Detroit in 1988.

But he wasn't present at the crime and didn't know that it would lead to the fatal stabbing of Pietro "Pete" Puma.

A University of Michigan law professor says Granholm had no authority to stop Makowski's release once she filed the papers.

State attorneys say the governor was free to change her mind.