Law enforcement agencies often use informants. Some informants work for money, but most are people who’ve been caught engaging in criminal activity. The vast majority of snitch deals are made by the police, who refrain from charging a suspect they’ve caught, in return for information or undercover work (typically, buying or selling drugs). A much smaller number of snitch deals are made by the police and the prosecutor together, when the suspect has criminal charges pending or is serving time. In these situations, the prosecutor lowers the charges or seeks to reduce the sentence, in return for information or undercover work.
It’s not worth it to law enforcement agencies to use snitches in investigating misdemeanors—they want information leading to felony convictions. In choosing a snitch, law enforcement agents look for someone who has significant criminal experience (a long rap sheet), because such a person is likely to have good connections and also seem relaxed and natural while participating in undercover work. Occasionally, officers will use a less-experienced snitch, if that person has a really good connection to the particular target of their investigation. A very productive snitch will be protected by law enforcement, to maintain him as a source of future information. An inept snitch may not be so lucky.
Informants can be very deceptive since they’re usually quite at home with the activities and communities they’re working on. In fact, an informant can be an old friend or acquaintance who only just recently happened to fall under police control. Even though you know that someone’s been quietly selling drugs for many years, there’s no guarantee that he hasn’t just as quietly become an informant in the past month. Some informants are prisoners (or cops pretending to be prisoners), put into the same cell as an incarcerated suspect. Just as with undercover officers, informants do not admit that they’re really law enforcement agents in disguise.