First of all, detrmination of whether or not it is actually accessory or a joint principle act. The test to distinguish a joint principal from an accessory is whether the defendant independently contributed to causing the "actus reus" (the act itself) rather than merely giving generalized and/or limited help and encouragement. In some jurisdictions, an accessory is distinguished from an accomplice, who normally is present at the crime and participates in some way. An accessory must generally have knowledge that a crime is being, or will be committed. A person with such knowledge may become an accessory by helping or encouraging the criminal in some way, or simply by failing to report the crime to proper authority. The assistance to the criminal may be of any type, including emotional or financial assistance as well as physical assistance or concealment.
If it is determined to be accessory, punishment varies from one jurisdiction to another. That being said...
The U.S. criminal code makes aiding and abetting a federal crime itself a crime:
(a) Whoever aids, abets, counsels, commands, induces or procures the commission of an offense, is punishable as a principal.
(b) Whoever willfully causes an act to be done which if directly performed by him or another would be an offense, is punishable as a principal.
A person may be convicted of aiding and abetting any act made criminal under the code. The elements of aiding and abetting are, generally:
(1) guilty knowledge on the part of the accused ( the mens rea);
(2) the commission of an offense by someone; and
(3) the defendant assisted or participated in the commission of the offense (the actus reus).
I hope you haven't done something you may regret. If you know anything, go to the police immediately. Even if you have knowledge that someone may do this, you can be charged if you do not go to the police. Also, if someone is injured or dies, you can be charged with attempted muder/manslaughter in some states. If it a firefighter, policeman, or paramedic and they die you can be charged with capital murder, which is punishable by death in some states.
Again, I urge you to go to the police, IMMEDIATELY. Good Luck, Susu



