The entire point of driverless cars is that the software of the car is superior to the wetware of the human. Humans cannot be trusted to determine what the car does, directly, under any circumstances, even an emergency.
So the answer is, you don't. The sort of fine-grained, always on surveillance necessary for driverless cars to work would be applied outside the cars as well as inside. Pedestrians are dangerous, with or without a gun, and as soon as you walk outside and attempt to interact with the urban environment without the safety of a self-driving car, someone would be alerted. Your identity will be confirmed, you will be tracked and every self-driving car for miles will know about it.
So in your scenario, the proper authorities have been called before you were even aware of his presence, simply because there was a human near traffic.
So the answer is, you don't. The sort of fine-grained, always on surveillance necessary for driverless cars to work would be applied outside the cars as well as inside. Pedestrians are dangerous, with or without a gun, and as soon as you walk outside and attempt to interact with the urban environment without the safety of a self-driving car, someone would be alerted. Your identity will be confirmed, you will be tracked and every self-driving car for miles will know about it.
So in your scenario, the proper authorities have been called before you were even aware of his presence, simply because there was a human near traffic.