"Hinrichs' backpack, which contained wires, a battery and a circuit board."
A timer? It wasn't suicide, his father's just in denial. This kid was gonna do something!
"Someone saw him fiddling with it (the backpack) shortly before the explosion occurred."
He was probably putting in the battery.
Could it have been on OCD despondent male who needed to make sure he died at 4:37 pm? :)