A midair collision between an Army helicopter and a jetliner killed all 67 people aboard the two aircraft, officials said Thursday, as they scrutinized the actions of the military pilot in the country’s deadliest aviation disaster in almost a quarter century.

U.S. authorities on Thursday (January 30) said it was not yet clear why a regional jet crashed into a U.S. Army helicopter at a Washington, D.C. airport, killing 67 people. Here's a look at what we do know about the incident.