Federal prosecutors frequently bring conspiracy charges. Conspiracy is a broad crime that can sweep up many kinds of conduct.
Conspiracy charges are challenging to defend. A federal criminal defense attorney who has a client who is charged with conspiracy has to be very diligent in investigating the government's evidence and what role the government thinks each person had in the conspiracy.
A conspiracy to commit a federal crime happens whenever there is an agreement to commit a specific federal crime between two or more people, and at least one of those people makes some overt act to further the conspiracy.
The government doesn't have to prove that there was a written agreement between the co-conspirators; instead, the prosecutor can prove a conspiracy just by proving that the people it says were involved in the conspiracy were working together to do some crime.
The general federal conspiracy statute is 18 U.S.C. § 371. This statute criminalizes both conspiracies to defraud the United States as well as conspiracies to violate any other provision of federal law. By the text of that provision you can see how the two elements work. The statute says that it is a crime,
[i]f two or more persons conspire either to commit any offense against the United States, or to defraud the United States, or any agency thereof in any manner or for any purpose, and one or more of such persons do any act to effect the object of the conspiracy.
The United States Code contains other specific conspiracy provisions. For example, 21 U.S.C. § 846 makes it illegal to commit a conspiracy to manufacture, distribute, or possess with intent to distribute controlled substances. Eighteen U.S.C. § 1951 – which prohibits committing a robbery of any article in interstate commerce – contains its own conspiracy provision. So section 1951 makes it a crime both to commit a robbery and to conspire to commit a robbery.
Courts have held that a person can be in a conspiracy with another person, even if the two people never meet or interact – as long as they knew the other person was doing something to further the conspiracy. This is most common in a larger sprawling conspiracy where a central person, or a group of people, is coordinating the work of many others.
Conspiracy charges have the potential to be abused by the government, and taken to absurd consequences – in theory, a conspiracy offense could be committed, and prosecuted in federal court, merely by having two people agree that they would rob a bank together and then buy a ski mask to wear in the bank robbery.
One vicious consequence of a conspiracy charge is that a very minor participant in a conspiracy can be swept up in the same case as someone who is much more responsible for criminal conduct. This is a particularly bad problem in drug conspiracy cases. For example, a person who had a very minor role in a drug conspiracy that involved a significant quantity of drugs can be subject to a mandatory minimum for all the drugs in the conspiracy.