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 Washington State, an accessory after the fact is someone who assists another person who has committed a crime, does so knowing that the crime has been committed, and acts with the intention to help the offender evade arrest or punishment. This is codified under Washington law, specifically in RCW 9A.76.175, which defines 'rendering criminal assistance.' The statute distinguishes between different degrees of rendering criminal assistance, which can range from a gross misdemeanor to a class C felony, depending on factors such as the severity of the crime committed by the principal offender and the nature of the assistance provided by the accessory. This is separate from being an accomplice, which involves participation in the commission of the crime itself. An accessory after the fact may also face charges under federal law for obstruction of justice if their actions are intended to prevent the apprehension, trial, or punishment of the offender. The relevant federal statute is 18 U.S.C. § 3. It's important to note that the penalties and treatment of an accessory after the fact can vary depending on the circumstances of the case.