A 17-year-old boy has admitted to opening fire during a botched robbery that he and several other Coffee County youths planned at school -- the attempted heist leaving one man dead and six others looking at the possibility of life behind bars.Sam Brinkley, 17, has reportedly admitted to police he was the one who opened fire Tuesday morning with an SKS assault rifle and killed Osbaldo Luna, 43, inside the camper in which he lived behind The Detail Shop on Beersheba Street. Luna also worked there.The military-style assault, complete with guns one of the youths said he took from his mother’s collection, was aimed at stealing what they thought was a large amount of marijuana held by Luna. That cache of drugs did not exist and there’s suspicion the victim may have been shot to death in his sleep.“There were shell casings all over the floor of the camper,” said McMinnville police detective Todd Rowland, who investigated the murder scene after the victim’s body was found by a relative Tuesday morning.