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Has any prior accident been caused by an psychologically unstable pilot?

Although it's not determined why the co-pilot of flight 4u9525 didn't (or couldn't) let the pilot re-enter the cockpit, the general assumption by the media is that it was likely a suicidal action on the part of the co-pilot. This made me wonder, I am aware a lot of psychological tests are given to pilots to prevent such a scenario, but those can hardly be perfect, so has any prior accident been caused by the conscious intention of one of the crew?