Runge is already in prison for the 1997 rape and murder of a Chicago mother and her 10-year -old daughter.
Runge was also charged with several other killings, including the murder of 25-year-old Stacey Frobel, who was a friend of Runge's ex-wife.
Prosecutors wouldn't comment Tuesday on why they dropped charges against Runge for the murders of Frobel and two other women.
