Two brothers aged 12 and 10 are feared to have killed themselves in a suicide pact using their father's gun.
Investigators believe the boys sneaked away from their home to a ravine before taking it in turns to shoot themselves in the head.
With police ruling out foul play they are working on the theory that the boys entered some sort of pact to take their own lives. The only other theory is that of murder-suicide.
'Whether it was murder-suicide, or suicide pact, unfortunately we’ll never know for sure,' said San Bernardino County Sheriff's Department Sgt. Frank Bell Bell. 'It’s hard to believe, to wrap your head around.'
Police said the boys had been told off by their father the day before the shooting for not doing their chores.
But police spokesman Sgt Bell said it was nothing out of the ordinary and both boys had been well cared for.
'The kids were well taken care of, and the house was in order,' Bell said. 'In everything we've learned in speaking to the family we can't find any reason that would cause these boys to be despondent to this level.