But this was a well-travelled highway. There was little liklihood that it would burn out before attracting attention.
This happened a 12:30 am ...midnight...might not have been any traffic...
A few minutes delay in getting help might have been enough. If as the previous poster said had the gas tank had gone, the damage would be much less suspicious. Perhaps a bad timer/detonator set it off at a less than perfect time.
It pretty clearly wasn't an accident.
With slightly different timing, or hitting, say, an oncoming car it sure would have looked like one.
We're not dealing with nice people here...