They cannot set up their own torrent. They can record IP of people that are already downloading the file from someone unrelated though. In the example the moment you offer someone crack you have entrapped them, they would have to ask you for it first. The idea behind entrapment is to not give someone the idea of committing the crime, it has to be their own. Then you have to prove intent. Just because a file is named something doesn't mean that the file contains what it is named.
I could host a torrent named toy story that was a movie about my kid playing with blocks. That is why they usually target people with multiple offenses, it shows a pattern.
Precisely, well, at least about the way they handle patterns.
The MPAA and RIAA is learning an individual who has uploaded a single copyrighted work, is easily fought in court. They go after the people who they have traced uploading multiple works. The users who just download also are rarely, if ever, pursued. But, downloading and not uploading in torrents, especially for the typical people who get caught, is something that user just doesn't understand most often. A lot of people use default settings on many different file sharing networks, and that often means many files are getting uploaded or they are uploading while downloading.
I'm curious to know if there are any recorded instances of the RIAA/MPAA going after people who use advanced techniques such as hitch-hiking on specific ports and using RC4 encryption.