I can see the author's point, but I wonder what would have happened if instead of finding the girl's body, they had traced the father's movements to some other crime for which he was not already a suspect. Could they then use that evidence against him? In this case, he was already a suspect, so surveillance was warranted.
I understand that this is not the same as a recording device because the recording device would allow the police to do something they normally would not have been able to do. So the traditional "wiretap" rules don't apply. There was no invasion of privacy. Still, the idea that the police can hide devices of any kind in your car bothers me. That's something that is open to abuse.
Interesting topic for debate. Nice find,
Theo.
EDIT: Wow. I just noticed this thread is almost a month old. Must have been dozing the first time it came around.