I don’t know much about his reasons, but based on the reliability of the Justice Department in the Clinton Years, it seems that most everything they did should be closely reviewed.
The ANFO/ANNM was supposedly mixed, transported - and detonated -- in blue plastic barrels. Fragments of blue plastic were found all over the area -- including atop distant buildings.
McVeigh's sketch of the truck's contents shows the three, empty, blue steel nitromethane drums placed standing next to the back door of the truck. Blast dynamics would have sent them up the street behind the truck -- and beyond the little red car whose hood was crushed by the Ryder truck's rear axle.
Yet, there has never been any mention of those three steel drums (or fragments thereof) being found and entered into evidence.
(...just one of myriad discrepancies in the OKBOMB "evidence" -- and the FBI's handling thereof...)