Ok I think the sheriff is RJ. He got the bomb with him in his hat. The
hat is lying on the couch all the time, even when the three guys with
the tattoos are lined up in front of Jane away from the couch area.
Now something happened, there was a gunshot, someone cried out 'no..'
Maybe
the only way out for RJ was to detonate the bomb. He knew he was far
enough from it not to be seriously injured. He caused the explosion and
made his escape somehow. Is it possible he planted his DNA at the site
to make it look like he died?
The bomb seems to have been near the couch area from the way the site looks after the explosion.