Prosecutors have turned to Michigan State Police as two law schools seek to overturn the conviction of a Detroit man who was 15 when he pleaded guilty to killing four people.

Wayne County Prosecutor Kym Worthy has refused to back away from Davontae Sanford's conviction — despite a hit man's confession to the same crime.

But on May 4, Worthy asked state police for "investigative assistance." The Associated Press obtained the letter through a records request. Lt. Mike Shaw confirms state police are involved.

The 2007 case, known as the Runyon Street murders, was handled by Detroit police.

Hit man Vincent Smothers confessed to police in 2008 but never was charged with Runyon Street. By that time, Sanford was in prison.

Smothers is in prison for eight other slayings.