Accomplice liability has been criticized on several grounds. First, it may extend the net of criminal responsibility too wide, punishing truly peripheral actors who did not play a significant role in causing harm. Second, it may punish a defendant more for her attitude than for the significance of her actions. Third, because the modern trend is to punish accessories just as harshly as principals, punishment may not be proportional to the defendant’s moral guilt. All accessories, including those who play very minor roles or whose help or encouragement may not have been needed, will be punished the same as those who actually commit the object offense. In short, standby actors can be treated as if they actually played leading roles.
The common law used fairly precise terms to describe individuals who could be responsible for crimes committed by others.
Principal in the first degree (P-1) is the individual who (1) personally commits the crime or (2) uses an innocent agent to commit a crime. Thus, the professional killer who actually commits homicide by shooting and killing the victim is a P-1. An individual can also be guilty as a P-1 if he uses an innocent agent to commit a crime.
Innocent agent is someone who (1) commits a criminal act but (2) lacks capacity to commit a crime or the mens rea for the crime and (3) is fooled or forced to commit the criminal act. An innocent agent is usually a person, but it can also be an animal or an inanimate object (such as a computer programmed to destroy files). A drug dealer who deceives a teenager into delivering drugs by telling him it is medicine has used an innocent agent to commit a crime. Or a dolphin trained to attach a magnetic explosive device to a boat that then explodes and kills the passengers would be an innocent agent. Both have committed a criminal act, but neither would be considered to have committed a crime.
The actus reus of the person delivering the drugs will be combined with the dealer’s mens rea to impose liability on the dealer as P-1 for the crime of delivering drugs. Likewise, the actus reus of the dolphin will be combined with the mens rea of P-1 to impose liability on P-1 for murder. Similarly, someone who is forced by another at gunpoint to commit a crime is an innocent agent; the coercer is guilty as a P-1.
Note that when someone uses an innocent agent to commit a crime, the law considers him a principal in the first degree and not an accomplice. The act of an innocent agent is not considered the act of the agent but rather the principal’s act.
Principal in the second degree (P-2) is the individual who intentionally helps or encourages P-1 to commit the crime and is actually present at the crime scene or is constructively present (i.e., near enough to assist P-1 if needed). P-2 could be the lookout who alerts the shooter to the victim’s imminent arrival or the driver of the getaway car.