You can do this, Son. Don't be nervous. It's just sunglasses.
The principal of a crime is the "leader" of a crime. They are primarily responsible for the crime. In this case, The bride with a knife in her back is the principal of the crime.
Accessory After the Fact
It will be fine. If they haven't caught you by now, they never will. ;)
The accomplice is someone who has a part in the crime being committed, but is not the principle. Even if the primary criminal is not charged, the accomplice can be. They also face lesser penalties than those of the principle.
Crimes of Ommission
Just going to pretend I never saw that...
A person who is an accessory before the fact is guilty of the crime as well. They are the ones who council or help the principal before the crime is committed.
An accessory after the fact is someone who tries to help comfort the principle of helps them hide what they did after the crime.
A crime of omission is when someone who did not commit the crime, but witnessed it, does not call authorities or take action when they themselves are not in any harm.
Preliminary crimes are crimes that have not been completed. The principal has made threats and/or steps to commit the crime, yet has not done it yet.
I'm going to kill you tonight! Be careful going out alone!