Myth 1: You Can't Be Tried More Than Once For The Same Crime
There are some exceptions.
Myth 2: The Government Can't Punish You For A Crime Without First Convicting You
Under federal sentencing law, once a defendant has been convicted of any federal crime, when determining a sentence, the judge can consider other crimes he or she may have committed. That includes crimes for which the defendant has never been charged and even crimes for which he or she has been acquitted.
Myth 3: Ignorance Of The Law Is No Defense
Every introductory criminal justice class teaches this one.
This particular "myth" is mostly true.
But there is one exception to this rule: If you work for the government, particularly in law enforcement, you can be forgiven for not knowing the law.
Prosecutors have absolute immunity from lawsuits related to the decisions they make about whether or not to charge someone with a crime, even when they are clearly wrong about the law.
Police officers and most other government employees don't enjoy the broad absolute immunity afforded to prosecutors and judges, but they do have what's known as "qualified immunity:"