( CNN ) A selfie taken by a homicide suspect posing with his alleged victim and later posted to the social media site Snapchat `` was a key piece of evidence that led investigators to the defendant , '' John Peck , district attorney for Westmoreland County , Pennsylvania , said Monday . The photo shows the victim , 16-year old Ryan Mangan , sitting in a chair with a gunshot wound to his face , according to police documents . A male taking the photo faces the camera with the victim behind him . According to the criminal complaint , Mangan was found dead by his mother last Wednesday after he was shot in the face inside his home . When police searched the home , they found a 9 mm shell casing but no firearm . A couple of days after Mangan 's body was discovered , police received a call from a mother whose son received a Snapchat photo from the suspect , 16 . The photo had the suspect 's first name across the top , and it matched the description of the crime scene . Peck says authorities plan to charge the suspect as an adult . CNN is not naming him because he is a minor and has not yet been formally charged . The mother said her son also received messages from the suspect that said , `` Told you I cleaned up the shells '' and `` Ryan was not the last one . '' Authorities executed a search warrant at the suspect 's home , where they found a 9 mm handgun in the basement hidden under the steps . Police say he confessed to using the firearm to shoot Mangan in the face and leaving him in his room . He is accused of homicide and a firearms count . A preliminary hearing for the suspect has been scheduled for February 19 . CNN 's Karan Olson contributed to this report .
Ryan Mangan was found dead in his home last Wednesday . Police say a homicide suspect snapped a selfie with Mangan and posted it to Snapchat . A 16-year-old will be charged with homicide and illegal possession of a firearm .