(Phoenix, AZ) -- A Phoenix teen is pleading guilty to killing two people in 2012. When Tyson Langley was 15-years-old he killed two people during a Peoria smoke shop robbery. Now 17, Langley is charged with second-degree murder and armed robbery. Police say the teenager left a note for his family explaining he was, quote, "leaving to become a man," before the incident occurred. His sentencing is set for late February.