Authorities believe that the Cleveland killer who posted a Facebook video of himself executing a grandfather has now turned off his cellphone, making it more difficult for police to track him, sources told cleveland.com.

A massive manhunt is under way for Steve Stephens, 37, who officials say posted a video of himself gunning down Robert Godwin Sr., a 74-year-old father of nine.

Cleveland police spoke to Stephens over the phone early in the investigation, but he refused to turn himself in.

A ping from his cellphone was detected in Erie, Pa., about 100 miles east of Cleveland, authorities told CNN.