Are you sure this boy was suicide? His arms are too short to hold the long shotgun, also suicide should not pissed like that if he decided to kill himself even 13 years old boy.
His boots and pants're so dirty and bolar, he might be knocked heavyly which caused urinary incontinence
on the head and moved into the room then be killed by the shotgun. Just say.
I remember seeing a WWII Japanese soldier who committed hari-kari using his toes to trigger his rifle... this kid obviously didn't use his toes, and I agree his arms seem way too short to have pulled it off.