How does a principal in the first degree differ from a principal in the second degree?

In the context of criminal law, the distinction between a principal in the first degree and a principal in the second degree centers on their level of participation during the commission of an offense:

• Principal in the first degree: This is the individual who actually performs the criminal act, such as the person who wields the weapon that strikes a fatal blow. In some instances, if a person uses an "innocent agent" (someone who commits the act without criminal intent) to carry out a crime, the person who caused the agent to act is considered the principal in the first degree.1
• Principal in the second degree: This individual is present—either actually or constructively—at the scene of the crime and assists, encourages, or incites the perpetrator, but does not perform the primary criminal act themselves. An example would be someone standing guard during an armed robbery or holding a victim down while another person strikes them.231

While common law historically distinguished between these roles, many modern jurisdictions treat both principals as equally responsible and subject to the same punishment.231