NEW : Seats removed from plane , fuel drum missing from airport . IRS takes lead role in investigation into Texas , Austin , crash . Pilot 's wife expresses her `` sincere sympathy to the victims and their families '' Art Acevedo believed to have flown plane into FBI building in suicidal attack .
NEW : Seats removed from plane , fuel drum missing from airport . FBI takes lead role in investigation into Austin , Texas , crash . Pilot 's wife expresses her `` sincere sympathy to the victims and their families '' Joseph Stack believed to have flown plane into IRS building in suicidal attack .