The 50-year-old was shot dead on Dec. 22 or 23, 2013, state police said in a release.
Mitchell was staying at a remote cabin he owned with his wife Dorothy at 157 Lake View Lane in New Albany, Bradford County, authorities wrote. Detectives said he was at the rear of the cabin with his dog when he was fatally struck by a single bullet.
Friends found Mitchell's body at the cabin after they had stopped hearing from him, according to police.
Authorities said Mitchell was a truck driver by trade who was out of regular work at the time of his death. He was earning money by selling items he repaired on Craigslist and "tinkering" with friends' vehicles, police said.
"The investigation remains active and new evidence has recently been discovered," said troopers.
Anyone with information is asked to call PSP Towanda at 570-821-4110 or submit an anonymous tip online via Crimewatch.
Click here to follow Daily Voice Bethlehem and receive free news updates.