All cameras record sound, getting one that does it well is more of a problem. Mainly it's a problem with recording while inside a waterproof case, where the sound is very muffled. Many cameras include a "skeleton door" - a back door with holes in it which allows better sound to be recorded.
I personally like my SVC200
Techmoan - Techmoan - SVC200 is the best £100 action camera I've found (So*far).
That's what I currently use. However I don't think there is a skeleton door for it. The assumption is if you don't need waterproof, you'll just mount the camera directly. That's a valid option.
It would be nice to get someone to ride along with you with a camera. Having both video and a witness might help.
However, it sounds like it may not matter if you have the Pope providing evidence - they're just not interested in helping you. The guy may be the cousin of the sheriff or something.
If that's the case, you may be forced to build up a large body of evidence including what the police said on each occasion (write down time/date and what is said on EVERY occasion) - then go to the press.
However, that's a lot of emotional strain. And in the end it may not matter if the paper is owned by someone who doesn't care either or is also related to the guy.