The last conspirator in a 16-member Centreville, Va.-based heroin dealing ring that left four teens dead was found guilty Tuesday by a jury in Alexandria’s federal court.

The other 15 members pleaded guilty, but 20-year-old Skylar Schnippel chose to go to trial for selling the heroin to his 19-year-old girlfriend Alicia Lannes that killed her in March 2008. According to prosecutors, Schnippel knew Lannes had overdosed in the past when he sold her the drugs.