Upon conviction a defendant to a federal criminal prosecution can appeal the judgment claiming that something was done improperly at trial. Appeals by the government are limited by the U.S. Constitution’s Fifth Amendment, which prohibits “double jeopardy.”
A proffer is a written agreement between federal prosecutors and a person under criminal investigation where the person agrees to give helpful information to the government in exchange for assurances of non-prosecution, lesser charges, or immunity.
A drug conspiracy is an agreement between two or more people to commit a crime. To obtain a guilty verdict, the U.S. prosecutor must have sufficient evidence to prove that there was an agreement between two or more people to violate a federal drug law and that all conspirators knew that they were agreeing to and joining in on a federal drug crime.
When a federal investigative agency, such as the FBI, the ATF or the DEA, feels they have sufficient evidence to suspect that you have committed a crime, they present their case to a federal magistrate judge.
If you get a knock on the door in the middle of the night, if agents appear at your workplace, if for any reason you feel you are under investigation by a federal investigative agency, you are probably right.