Complex sentence: Purley later stated he could hear Williamson's screams from underneath the car, but by the time the first fire engine arrived and the fire was extinguished, Williamson had died of asphyxiation.
Split into simpler sentences: Purley later stated he could hear Williamson's screams from underneath the car. By the time the first fire engine arrived and the fire was extinguished, Williamson had died of asphyxiation.