15-year-old steals assault rifle, unintentionally shoots himself in the head

Three teenagers from Houlton, Maine, ages 13, 15, and 18, broke into Mac's Trading Post on Tuesday night. They used a rock to break the glass in the front door and then used a hunting rifle from the store to break the glass in the display case. They stole two assault rifles and two .40-caliber semiautomatic handguns from the display case, and also took 100 rounds of ammunition for the assault rifles.
According to police the boys stole the guns because they planned to use them to rob a bank. While the 15-year-old was loading one of the assault rifles in preparation for an armed confrontation with police, he unintentionally discharged the gun, shooting himself in the head. The bullet grazed his forehead and scalp area. When police arrived they found him conscious but bleeding profusely from his injury. He was taken to local hospital and then transferred to a regional medical center for treatment.
Police were able to recover all the guns and ammunition. The 13-year-old and 18-year-old have been taken into custody and charged in the burglary. The 15-year-old is still in the hospital and hasn't yet been charged.
Ohh shoot.