The 16-year-old boy is accused of murdering Ryan Mangan, 16, at his home in Jeannette, Pennsylvania, on Wednesday.
He was arrested after police were given a copy of the photo, which had been sent to another boy through the phone app that automatically deletes messages within seconds unless they are saved.
“(Police) received a copy of the photo which depicted the victim sitting in the chair with a gunshot wound to the face,” said an affidavit seen by the Pittsburgh Tribune Review. “It also depicts a black male taking the ‘selfie,' with his face facing the camera and the victim behind.”
The mother of the boy who saved it contacted police, the newspaper reported, saying her son also received text messages saying “I told you I cleaned up the shells” and “Ryan was not the last one”.
The suspect has been charged with first-degree murder, homicide and possession of a firearm by a minor.
Ryan, who went to Jeannette High School with his alleged killer, is being buried today.
A GoFundMe page set up by a family friend in the wake of his death has so far raised more than $5,000 (£3,000) to help his family with funeral costs.
