What primarily defines an accomplice in criminal law?

An accomplice in criminal law is primarily defined as a person who assists or facilitates the commission of a crime, often with the intent to aid the principal offender. The correct answer accurately identifies this role by indicating that a principal who testifies against another principal can be considered an accomplice, as they were involved in the criminal activity, whether directly or indirectly.

This acknowledgment of participation is crucial because accomplices can share liability for the crime, even if they did not directly commit the act. In legal terms, it marks a significant distinction where an individual actively engages in or supports the crime, which differentiates them from those who are uninvolved or only offer indirect support, like those providing legal representation or advice. The answer emphasizes the relational dynamics within criminal offenses where an accomplice's role can significantly influence the outcomes of legal proceedings.