An accessory after the fact is a person who (1) assists someone who has committed a crime, (2) after the commission of the crime, (3) with knowledge that the person committed the crime, and (4) with the intent to help the person who committed the crime avoid arrest or punishment. The United States Code defines an accessory after the fact has someone who knows a crime has been committed and receives the offender (harbors them), or relieves, comforts, or assists the offender in order to hinder or prevent the offender’s apprehension, trial, or punishment.

An accessory after the fact is different that an accomplice to a crime, who helps with the commission of the crime. An accessory after the fact is treated as a criminal offense separate from the criminal offense of the offender being assisted, and may be prosecuted as the criminal offense of obstruction of justice.

In Pennsylvania, an accessory after the fact is someone who assists an individual who has committed a crime, knowing that the crime has been committed, and does so with the intention of helping the offender evade arrest or punishment. This assistance can include actions such as harboring the offender, providing comfort, or any other form of aid that might impede the offender's apprehension, trial, or punishment. The distinction between an accessory after the fact and an accomplice is significant; an accomplice is involved in the commission of the crime itself, whereas an accessory after the fact becomes involved after the crime has been committed. Being an accessory after the fact is a separate criminal offense and can be prosecuted under the laws pertaining to obstruction of justice. The specific charges and penalties can vary based on the nature of the underlying crime and the degree of assistance provided to the offender.