I believe Charlie Sheens done this before

Rating: 5/10 (14 April 2005)

If I hadn't seen the biker flik - I would have given this a higher rating. But its five years on, Madsens still in it, and the idea of a cop infiltrating a group of misfits, conditioned to do his duty at the same time as mingle with the criminal element, and then adjust to the new identity, is an age old storyline Yeah there are the greats in the film, yeah the main actors do their best to follow a script based on a true story, yeah there's an element of action and horror that keeps the audience watching to the end. But the portrayed story of this is soooo close to Chasing the Shadow, that I would have thought that anyone trying it again five years down the line would have adapted it accordingly for real originality (if you can make U571 or The Patriot, then anything is possible to make an original storyline appeal to the masses).
I do like Pacino and Depp in a lot of productions, but this one has the elements of bringing them together because, well, they had to appeal to the young and older audience to make a blockbuster.
Go have a look at the 1992 one with Mr Sheen, its more in line with a true story (it doesn't have sawing people into pieces though), and it works better for me as its got the reality of dealing with two ends of the legal spectrum.