DENVER: Heralded as the star witness for Timothy McVeighĺs defense, Daina Bradley was expected to give testimony that would virtually prove that he was nowhere in sight moments before the bomb destroyed the Alfred P. Murrah federal building two years ago. But she shocked a packed courtroom Friday by changing her story midway through her testimony, saying she saw two men scurry away from the Ryder rental truck parked outside the building just before the blast, rather than just the one olive-skinned man she had told investigators about earlier. A visibly shaken Bradley, who lost two children and her mother in the explosion and had a leg amputated to remove her from the rubble, also admitted that she told defense lawyers only a week ago that she saw a second man, whom she described as a white male, leave the truck but that the man was not McVeigh. Then the 21-year-old woman changed her story again, saying she had later told prosecutors she simply was not certain whether he was McVeigh. Bradley admitted that from age 7 to 16 she had undergone psychiatric treatments in mental institutions, where she was given large doses of drugs that caused her ''to lose memory of who I was and (of) people around me.'' During cross-examination, Bradley acknowledged her contradictions but said she was sure of one thing: there were two men. She added that she did not recall much after the bombing. ''You could tell me one thing one week and I would forget the next week,'' she said. Bradley's dramatic testimony came as a major blow to the defense, eliminating a key support for their theory that someone other than McVeigh had to be the bomber.