and they hadn't been able to stop it

was that a car with automatic transmission? If not, you can stop the engine by hitting the brakes and shifting to the 5th (or 4th) gear.

I needed this long ago with my Alfa Spider, when the gas got stuck at full throttle.
My first thought was about those film-scenes, when someone races down the streets and can't stop the car.
Then i cleared my mind and just hit the brakes...

cheers, Thomas