I think McVeigh is the hardest element to get a clear read on. The nature of truck bombs is what sells me on feds. His design results in most of the force going up, not out. Even with 10x the volume, a fertilizer bomb is unlikely to do significant damage to a concrete column adjacent to it, let alone a dozen, hundreds of feet away, through walls. And most importantly: supposedly, the severed columns were not equidistant from the truck.

If the truck didn't do the job, OKC was demo-ed. How McVeigh fits into all this becomes trivia at that point.