They're the people in the white cars with blue flashing lights, carrying handcuffs, and wearing stern,serious expressions. Easily recognised by a partial or complete personality bypass.
Personally I wouldn't bother with the police. Go to F.A.C.T (Federation agaist copyright theft) http://www.fact-uk.org.uk just fill in a form and you're done, I think they also offer rewards if they prosecute from your information.
If you're not in the UK then I don't know!