accomplice witness

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An “accomplice witness” is someone who is both a witness to a crime and an accomplice in that same crime; one who participates with the defendant before, during, or after the commission of the crime. The participation must involve an affirmative act or commission by the accomplice witness to promote the commission of the offense. However, a witness is not an accomplice witness simply because they knew of the offense and did not disclose it, or even concealed it. 

Depending on the extent of their participation, an accomplice witness may be charged with principal in the second degree, accessory before the fact, or accessory after the fact

Generally, under the Model Penal Code (MPC), the mens rea required for accomplice liability is to have the purpose of promoting or facilitating the commission of the crime. The actus reus required for accomplice liability under the MPC is assistance in the commission of the crime. While mere presence is insufficient to establish actus reus, qualifying assistance include solicitation, encouragement, aiding, attempting to aid, agreeing to aid, and omission

There is no need to prove that the accomplice is but-for or proximate cause nor whether the accomplice witness’s conduct has any causal link to the principal in the first degree’s conduct so long as the mens rea and actus reus are satisfied.

An accomplice witness may be convicted of criminal attempt even if the crime was neither committed nor attempted by another, so long as the purpose of their conduct is to aid another in commission of the offense and such assistance would have made them an accomplice if the offense were committed or attempted. 

Under common law, the state must prove that the underlying crime was committed by the principal in the first degree in order to establish accomplice liability. Qualifying assistance under common law include solicitation, encouragement, active assistance, and omission. 

[Last updated in December of 2021 by the Wex Definitions Team]