On December 7, 1987, Pacific Southwest Airlines Flight 1771, carrying 38 passengers and 5 crew members, departed from Los Angeles for what should have been a short flight to San Francisco.

Moments after reaching the standard cruising altitude of 22,000 feet, the pilots inside the aircraft signaled distress, telling air traffic controllers that shots had been fired. The airplane was sent falling down to the ground almost breaking the speed of sound.

All 43 people on board Flight 1771 were killed.
Was this some tragic accident, a malfunction in the aircraft? Or did someone intentionally cause that PSA flight to crash?