Anna Merriman | For NJ.com
Mehn appeared at a detention hearing after a judge ruled last week he would be tried as an adult, Mercer County prosecutors said Wednesday.
Mehn is charged with murder and weapons offenses in the September killing of Keyauna Hughey. Superior Court Judge Peter Warshaw ordered he be held without bail.
Mehn has been in custody on the charges since September but he was not identified until his case was moved up to adult court.
He was one of three suspects believed to be involved in the shooting; one of the suspects is still at large and another, Raekwon Fulmore, 21, was charged with hindering apprehension last year for his part in the case. Mercer County prosecutors have said they believe Mehn was the gunman in the case.