Earlier quoted context omitted.
I don't know. Apparently a lot of the people here are master criminals, because they seem to be awfully paranoid about the idea that police detectives can, if sufficiently motivated, deduce some information about their activities. (These sorts of folks must really hate Sherlock Holmes stories.) Personally, as a law-abiding citizen, I'm really not too concerned about being the target of a police investigation, and if…
You assume that the police care if you are guilty or not. They don't. The quality metric that police work towards is not finding the actual perpetrator, it is finding someone who can be convicted, or, even better, strongarmed into confessing and/or accepting a plea bargain. As a (mostly) law-abiding citizen myself I wish it were otherwise. But it isn't. See e.g. http://www.youtube.com/watch?v=6wXkI4t7nuc
(Edit: The question's phrasing is for effect; I'm well aware there are egregious abuses documented in number greater than one. But I'm still not convinced that with the non-uniformity of the LEO population between different jurisdictions, etc, as well as the non-random selection bias, that all the accounts we have of LEO malevolence provide statistical certainty that police, overall, are bad.)