Do not EVER turn off your engine if your accelerator is stuck at full throttle. Had the police officer mentioned in the OP had done that, this is what would have happened:
The steering wheel would have locked, therefore, not able to steer the car, which means that a huge 100+ mph rear impact is almost certain, causing a multi-car crash that would have probably killed even more people.
If your car is stuck at WOT, shifting into neutral is probably the best course of action. However, given that the brakes were already destroyed on the car, it is quite possible that even if he HAD done this, the result may not have changed.
What baffles me is how can it be that Toyota, often a pioneer of technology used in automobiles does not have an electronic failsafe in the event that both the brakes and accelerator are depressed simultaneously. This should be standard on EVERY automobile from EVERY manufacturer. If it's not, I expect by the next MY, all vehicles will have this feature, regardless of manufacturer.