Police say a Logan County man convicted of killing a grocery store clerk and his pregnant wife 35 years ago has died in prison.

56-year-old Russell Smrekar died at Menard Correctional Center from a medical condition.

Smrekar was serving a 300-year sentence for shooting Lincoln grocery store clerk Jay Fry and his pregnant wife, Robin, in October 1976. Authorities say Jay Fry was killed after witnessing Smrekar stealing steaks at a Kroger; his wife was killed because she witnessed her husband's slaying.

Last month, Smrekar confessed to killing Ruth Martin of Lincoln because she also saw him stealing. She disappeared in June 1976.

He also said he killed Lincoln College student Michael Mansfield of Rolling Meadows in 1975. Mansfield disappeared six days before he was to testify in another case in which Smrekar was accused of burglarizing a dorm room.