His body was there....a bit of speculation to assume he was alive when the explosion happened....or is there some way to prove this person was alive when they got blown up??
There were reports of gunshots heard shortly before the explosion. Perhaps he started up the pre-recorded soundtrack and timer, then shot himself. He may have been a conspiracy nut, but he was no jihadist.
Unless they get lucky and find a piece of skull with a bullet hole in it, probably not. I think he probably drove the RV down there and killed himself (gunshots) after setting up his device with a timer to run the announcements and detonate the bomb.