The Differences Betweeen Fictionalised and Real Police Investigation?

There's all these police investigation shows on tv at the moment (all the different CSIs, etc). I'd like to see a documentary that looks at how their potrail of police investigation differs from the reality.

I think that could be quite interesting (and I say this even as someone who's not really into those shows). Surely, there are differences; but how many, and in what ways? It would be interesting to know this in concrete detail.

And it would probably do us some good, as I imagine that for a lot of us, our main conception of police investigation comes from such shows.

I have no idea whether there is anything like this out there.

(and of course, a similar idea could be applied to medical dramas, etc).