What was the possible reason for the shuttle disaster?

NASA’s brightest investigators have toiled for six months to find out what caused the shuttle disaster. (29) The leading theory was that a block of foam fell from the external tank and was so severely that Columbia could not reentry. Today, in the most dramaticTEST so far, (30)NASA simulated the forces at play. The foam, fired at 500 miles an hour into the reinforced carbon tunnel of a shuttle wing. The results left investigators astonished but also relieved. They now believe they’ve proved their theory of what caused Columbia to disintegrate high above Texas on the morning of February 1st with the loss of all seven astronauts aboard.