This photo, taken moments before the crash, shows that the P-51 had lost its left elevator trim tab. (I've circled the spot where the trim tab should be.) Without the trim tab, the aircraft may have been uncontrollable.
(Original Photo by Tim O'Brien, Grass Valley Union (AP).)
Why did the aircraft lose its trim tab? One possibility is "flutter," an aerodynamic phenomenon that can, once it starts, damage a control surface quite suddenly. Here's a NASA video of flutter in action.
An aircraft is at risk of flutter when its airspeed pushes up against or exceeds its design limits.
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