There were numerous surveillance tapes that were confiscated by the FBI that substaniated the eyewitness testimony stating that there was another man with McVeigh in OKC on the morning of April 19th. These tapes have been intentionally withheld from the public by the FBI. They were not shown to the Federal Grand Jury or at the trial. In fact, the prosecution did not present at trial a single eyewitness that placed McVeigh in OKC on the morning of the bombing, even though there were many witnesses that saw McVeigh that morning. Some picked him out of a line up.
The problem was that each eyewitness that saw McVeigh saw him with another man, John Doe 2, and so the prosecution did not present the eyewitnesses at trial or the videotapes showing McVeigh at the Murrah Building with John Doe 2.