Wow, good damn idea but you know, they make spy cameras real small with audio, that would have been much better, no trying to explain who said what when and where.
But the voice recorder is a good stepping stone, but if that's all I was using I'd make sure it makes super high quality crystal clear recordings. My iphone 4 will record for up to an hour, I've used it before to monitor my car while it was parked at work. I am seeking a dvr system with 4 cameras and motion sensors which will record while it's off if I choose (for vandalism).
Put it on Youtube, everybody in your area will see this, try to get local news on it. The leverage you have is all about going public with it, they'd have to take care of you fairly and let it be known the jack-asses that did that were fired. Of course don't just threaten to do it, do it and let them know, they already did the damage, now it's your turn.
So what made you suspect that you'd find something like this on your voice recorder? Was it just reading gestures, body language, how you were treated during past dealings, or did you hear rumors they were scumbags? Sickning!!
Correct me if I'm wrong, but isn't there laws against malicious destruction of others property, and when it's over a certain amount, isn't that a felony
and a valid right to file a case with your local police?
The beauty of using a security camera is that they are date and time stamped, which I hear is an important factor in a legal situation for it to be used as evidence. BTW, if they KNEW that your car had cameras and audio, and they were not to tamper with them, they'd never have done that crap in the first place.