I've just got two questions, and there may well be good answers as I have not been involved with this issue. Why did McVey continue to say they acted along until his death and why doesn't Nichols say anything now?
Part speculation part fact -
Tim Mcviegh has a sister who was facing prosecutorial pressure, which did not materialize (fact).
TM cared deeply for his sister (almost fact).
Speculation: TM acted the way he did after the bombing to protect his sister.
Speculation: TM acted the way he did after the bombing because he realized that he was manipulated into being the fall-guy/triggerman for an islamic plot to attack the US. He did not want to go down in history as being a dupe, but instead someone that acted for his own cause (which in a warped way he believed was just).