We all do it, probably without even knowing it most days. We'll stand in a bank line and look at the cameras and wonder if they would catch us if we walked out with a hundred grand. Or maybe you're working the cash register at a store and occasionally think about slipping a bill into your pocket? When does thinking about a crime turn into committing a crime.
There are three requirements to prove a conspiracy:
1) Two or more people,
2) An mutual agreement to commit a crime, and
3) An overt act in furtherance of the conspiracy.
The first element is simple. It takes at least two to make it a conspiracy. Otherwise, if the person comes close enough to committing the crime, it is an attempted crime.
The agreement is trickier. What exactly is an agreement? Does it have to be in writing? Oral? What if one of the suspects cannot be prosecuted for the crime because they are mentally challenged? Or an undercover officer?
The agreement can be in any form - oral, written, or otherwise. To prosecute these cases, we always seek some corroboration of the agreement like a letter written between the suspects or, where one is cooperating, a recorded conversation. A person can still be guilty of a conspiracy if they commit the crime with someone who cannot be prosecuted for it. An example to demonstrate - The suspect wants to have her husband killed for the life insurance. She doesn't want to do it because then she won't get paid. She seeks someone else. The police get wind of it and send an undercover officer to speak with the suspect. The undercover officer wears a wire and records the conversation. Obviously, the undercover will not be prosecuted for the crime, and, therefore, the conspiracy charge will only prosecute one person. The law is clear that the suspect can still be charged with conspiracy even when the other parties cannot.
What constitutes an overt act? This is what moves it from bragging stages to crime. One of the parties who agreed to the crime must take at least one step towards its completion. Examples - buying guns, making a down payment to a contract killer, renting a getaway car, casing the location of a robbery. Any act that moves the conspiracy closer to completion will do. As a prosecutor, it is difficult to make the call when there are enough overt acts to arrest, but before the completion of a crime. What constitutes probable cause does not always persuade a jury that the group was serious about committing the crime. The overt act element is the line between Minority Report and protecting society.
Once all three elements exist, we can make an arrest. The only viable defense to the conspiracy must happen before the arrest. One of the participants must affirmatively withdraw from the conspiracy before the crime. This means they tell the other participants they are out and then they tell law enforcement. That is usually the way law enforcement finds out about the crimes. Participants become informants when they realize that the planning between friends is quickly becoming a criminal reality.
The federal government charges conspiracy much more than state prosecutors do. It can be charged in any case where co-defendants committed a crime, in addition to the completed crime charges. State prosecutors usually only charge conspiracy where there is an undercover investigation and an arrest before a crime occurs. They are some of the most satisfying cases because you are stopping the defendant before anyone is hurt. We don't get to do that often.