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.

The National Transportation Safety Board says the helicopter must be recovered from the Potomac River so it can get more precise data.

Crews working at the site of the deadliest aviation disaster in a generation have recovered all 67 victims of the collision between two aircraft over the Potomac River in Washington, DC, officials said Tuesday.

The Army helicopter that collided with a passenger plane above the Potomac River boasted an experienced crew doing “an unforgiving job.” Friends and relatives are still baffled and mourning their loss.

Radar evidence proves that the Black Hawk helicopter was not flying low enough during collision with American Airlines Flight 5342.