The Michigan Supreme Court says governors cannot reduce a prisoner's sentence and then change their mind, a ground-breaking decision that reverses one of Jennifer Granholm's last acts before she left office.

Granholm in 2010 commuted the life sentence of Matthew Makowski, making him eligible for parole after more than 20 years in prison. But she did an about-face within 48 hours and her order was destroyed.

It's an unprecedented case in Michigan. Lower courts let Granholm's decision stand, but the Supreme Court on Tuesday said she exceeded her authority.

Makowski was convicted of first-degree murder for arranging the robbery of a Dearborn health club co-worker in 1988. Makowski didn't know the robbers would be armed and wasn't present when Pietro "Pete" Puma was fatally stabbed.