"Since he was the biological father, I never thought it was him myself. Very rare."
Not in todays world. Remember the case that just occurred a month ago in Illinois. The biological father killed his own daughter and her friend in the park because she took money from her mothers purse. IMO these people are worst case scenario degenerates.
Maybe the boys were "bad" and someone put them in the hot trunk of the car to punish them. Left them in there for 4 hrs (OR MORE) and when they opened it, the poor kids were dead.
sw