I helped out a little and talked to a few people right at the scene. Here is what I saw and heard, and what it led me to believe:
I saw the guy's rope on the wall after he fell. It ran through commercially sewn draws on the first through fourth bolts.
On the fifth bolt was a single, apparently closed and intact carabiner of different color than the others on the route. I also saw this myself.
An intact carabiner was apparently found on his rope. I heard this from a witness.
I saw a piece of 1" blue webbing on the ground in the fall zone. It looked shiny and new, showed no signs of abrasion, and had hot-cut marks from a cutting machine or lighter at both ends.
The bolts were evenly spaced.
The belayer was not making himself known to anybody, or saying what happened, but he also wasn't lying on the ground dead of rockfall.
Dude looked like he weighed around 200.
What seems likely to me:
Guy clipped his fifth bolt with a hand-tied draw (the webbing), climbed some distance above it, then fell. His fall pulled the knot out of his webbing, leaving one biner on the rope, one on the rock. The force generated by what had become a 20-foot-ish whipper could easily have pulled an unprepared belayer off his stance, causing him to drop the leader in a barely controlled fashion to the ground.
With the bolt spacing, if he blew the sixth clip, his fall to and past the fourth bolt could have been as much as 20-25 feet. This alone would not have put him on the ground - I didn't measure distances, but it was obviously much further from the fourth bolt to the ground than it was from the fourth to sixth bolts.
The only funny thing was that the blue webbing I saw looked mighty short to tie a draw with - like, the biners would have been nearly touching. But no-one mentioned anything about seeing other broken webbing around, and neither of the biners apparently had half a broken QD attached to them.
Anyway, that's my armchair quarterback version of the facts, and what they led me to believe. Certainly made me plan on buying a GriGri.