During takeoff, the plane was observed to rotate to a steep nose high attitude, then roll into a steep bank, go into a descent, and crash. During the descent, it rolled to a wings level attitude before impacting with the nose slightly down. An examination of the flight controls revealed no preimpact malfunction or failure except that the elevator trim was inoperative. The elevator trim was found in a nose down position. The owner reported the trim button was inoperative, so it would have been set manually. The pilot's seat failed during impact. Impact marks revealed it was in the 9th position from full forward which was 9 1/8 inches from the front of the seat track to the front roller. The 13th position would have been full aft. The investigator was about the same height as the pilot. He reported he could move the control wheel and rudder with no problem when checked with the seat full aft in a similar aircraft. The pilot had only one other flight in that make and model as PIC.