Someone who assists another 1) who has committed a felony, 2) after the person has committed the felony, 3) with knowledge that the person committed the felony, and 4) with the intent to help the person avoid arrest or punishment. An accessory after the fact may be held liable for, inter alia, obstruction of justice.
Illustrative case law
See, e.g. Com. v. Dalton, 259 Va. 249 (2000).