Criminal law after the fact

However, if the defendant was not present, they are an “accessory before-the-fact.” An accessory after-the-fact is someone who, knowing a crime was committed, receives, relieves, comforts, or assists the offender or in any manner aids them to escape arrest or punishment.
See:

Finally, in Calder v.
Bull, the court expressly stated that a law that "mollifies" a criminal act was merely retrospective, and was not an ex post facto law. Scholars have argued that, as a historical matter, the phrase ex post facto referred to civil as well as criminal laws.

A “ crime ” is any act or omission in violation of a law prohibiting said action or omission.
Each state decides what conduct to designate a crime.
As such, each state has its own criminal code .