Mims, 69, died Monday in a state prison in Faribault, Sarah Berg of the Minnesota Department of Corrections said.
An armed gang of eight, led by Mims, robbed a Philadelphia furniture store on Jan. 4, 1971, tying up and beating 20 employees, two of whom were shot, one fatally. They then attempted to burn down the store in a crime then-Police Commissioner Frank Rizzo called "the most vicious I have ever come across."
While serving a life sentence at Graterford, Pa., prison, Mims allegedly arranged for drugs and prostitutes to be smuggled in, and held authority as imam of the prison's 1,800-member Muslim population, The Philadelphia Inquirer said.
In 1995, he was transferred to the Minnesota prison because he held too much influence over other prisoners, authorities said.