Unfortunately there is always a bad apple in every barrel. sometimes several.
I know one of my own sons had been the target of a couple of bad eggs in our local police department. This little digital recorders can come in handy when you have a bad cop hassling you.
This happen in Houston with a Metro Police Officer. The cop was caught red handed talking trash. All the stations covered it and then it quietly went away.
Maybe this is an idea that could assist your son...if it’s possible, I’d say go for it... I never thought of this before, but it is a great idea..I mean, cops are doing it supposedly to protect themselves against unsubstantiated claims, why not citizens do it for the same reason. There has got to be a way to subtly click a button and start the *hidden* camera rolling before the cop(s) approach the car.