Investigators trying to determine what caused last week’s deadly midair collision between a US military Black Hawk helicopter and an American Airlines plane near Washington, DC, briefed lawmakers Thursday on what they’ve learned after combing through data from both aircraft and air traffic control.

An American Airlines flight carrying 60 passengers and four crew members collided in mid-air with an army helicopter in Washington DC leaving no survivors, rescuers say. So far 28 bodies have been recovered from the freezing waters of the Potomac River.