PIERRE, S.D. (AP) — The South Dakota Department of Corrections says a man serving life in prison has died following an illness.

Corrections officials say 64-year-old Garreth Gannon, who was convicted of attempted murder and robbery, died on Wednesday in the infirmary at the South Dakota State Penitentiary.

Gannon pleaded guilty in April 1996 to shooting a Rapid City tobacco shop employee. At his trial he acknowledged that he was a career criminal who had spent the majority of the previous two decades behind bars.