There are a few common misnomers about officers woking undercover. It is commonly believed that

1. officers have to identify themselves if asked. They do not. In fact, they are free to lie about their identity, occupation, etc.

2. officers cannot commit crimes while they are undercover. They can. If you thought smoking out with someone or committing vandalism, or whatever, proves someone isn't a cop, you're wrong. Cops may commit crimes while undercover.

For more information on police techniques, check out the book "Beat The Heat," published by the Midnight Special Law Collective. Their website is www.midnightspecial.net/ and has tons of great information about your rights and police shananigans.