True. But the details of his confession are pretty damning.
So was the detailed sketch of the second person who was with McVeigh when he picked up the rental truck in Oklahoma City. But then some FBI/DOJ folks talked to the people at the rental agency after arresting McVeigh and somehow after that they didn't remember the second guy anymore, and McVeigh supposedly drove both his car and the rental truck home by driving one and then walking back to get the other one.
Strangely, years later a person who looked just like the person in the sketch from the Oklahoma City rental office was arrested and imprisoned for supporting terrorist groups.
"Details" in a document generated by the FBI/DOJ may not be entirely accurate - like the signed declarations used to get the FISA warrants against Trump's associates almost ten years ago.