Willeford reportedly shot and wounded Kelley outside the church, before the car chase. Then, according to the Sheriff, he took his own life. I suspect the key reason he crashed his vehicle was because he was wounded. Then, being the low-life coward that he obviously was, shot himself to avoid facing the consequences of his sick cowardly actions.
But if killer escaped. Was found an 20 minutes later calmly eating a big mac..plumber could not go in and just execute him in mcdonalds...even in texas.
Circumstances matter
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.