classes and turned over the tape to the fbi. the fbi says that professor's actions proved crucial to their investigation some six years later. on a hunch, la blanc asked agents to show ha video of him to sa save. >> from that video he was able to make on identification. >> reporter: on 9/11, his mother, who doesn't want to be named, says he called home for the last time. >> he called me and said did you hear what happened, so on, so on. they said they put it on the muslims. i said yes. i tell him do not come. and do not come. because the all against the muslim people. he was arguing with me. he say no, i didn't do nothing. i will come. don't worry about it. >> reporter: his mother adamantly denies her son is directing al qaeda attacks. but when i asked about the admitted times square car bomber, she said this.