Govt credibility is wrapped up in McVeigh acting basically alone. Bin Laden could release video of himself french kissing McVeigh and the govt would not change its story or release any new evidence at this point.
Whether this particular allegation is true is a separate question. (And one I don't claim to be able to answer).
"Bin Laden could release video of himself french-kissing McVeigh and the govt would not change its story..."And they would have plausible deniability. What with the current technology for falsifying images. Of course, bin Laden having access to such high tech stuff in his cave in Afganistan is a bit of a stretch, but such minor details never stopped the government before.