I'm going to go out on a limb here and say that he succumbed to the wound that the citizen inflicted on him which is why he crashed. It will come out later that there was no self inflicted wound.
I say this because of the vague way these reports are worded. That and because the media desperately don't want the good guy with the gun to be the cause of his death.
Exactly - the MSM will do anything to suppress the possibility that an armed citizen prevented an even greater tragedy. Thus the (unsubstantiated) narrative pushed by the MSM that the killer “committed suicide.”