The trunk of the vehicle was open. Without warning/reason, a support bar that helps hold up the open liftgate popped off and the liftgate swung closed rapidly with its full weight, not supported by anything. The support bar that had popped off obstructed the path of the falling liftgate, causing damage to the trunk panel. The speed at which the liftgate fell at full force could have caused severe injury or death. This has not been confirmed by a dealership or anyone else- this just happened today and I have not had it looked at by anyone yet.