There isn't a readily accessible, easily identifiable "fuel cutoff switch" like you might find on some other vehicles on a BMW 735i (or most modern cars for that matter). Modern fuel systems are electronically controlled, and shutting off the fuel is done by the car's computer system as part of the overall ignition system. There's no individual switch to manually interrupt fuel flow in an emergency.
If you need to disable the car to prevent it from starting, disconnecting the battery's negative terminal is the most effective way to achieve this.
