Simply remove all user controls, or lock them unless an authorized user is sitting in the seat.
If the vehicle stops for an 'emergency' reason, notify someone in central command immediately. At that point they can monitor the situation.
If the vehicle is stopped under an emergency, and notices that its door panels are being broken into, then it can notify central command so they can call the police.
All the while, it's recording from every angle possible.
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On the other hand, regular trucks have a driver who has to leave the vehicle to take care of human business and can be kidnapped or threatened into any number of actions that'd help a robber complete their work.
(Do military drones already have this? Could trucking companies legally send in armed security drones when they detect a robbery in process?)
I guess they'll just wire the truck to alert police and turn on lots of cameras. Police might respond quickly... at least until the number of false alarms (truck hits a hole a bit too heavy, alarm goes "ROBBERY!!!11!") stays low enough.
The only thing that stops a bad guy with a gun is a good AI with a gun