Vincent Smothers admitted in Wayne County Circuit Court on Monday that he killed 47-year-old Rose Cobb on Dec. 26, 2007. He says he was hired to kill her by Cobb's husband, David Cobb.
David Cobb was never charged and hanged himself in September 2008.
Smothers is also charged with killing seven other people as a hired gun and is in the process of accepting plea deals in those slayings.
Smothers would serve a minimum of 50 years in prison for second-degree murder.