One of Prof Librescu's students, Alec Calhoun, who was with him at the classroom when the shooting started, told AP that at about 9:05 am, he and classmates heard "a thunderous sound from the classroom next door, what sounded like an enormous hammer."
When students realized the sounds were gunshots, Calhoun said, they started flipping over desks for hiding places. Others dashed to the windows of the second-floor classroom, kicking out the screens and jumping from the ledge of the room.
Calhoun said that just before he climbed out the window, he turned to look at the professor (Librescu), who had stayed behind to block the door.
Via Pajamas Media.