(A) A private person who makes or assists another private person in making a lawful arrest is justified in the use of any force which he or she would be justified in using if he or she were summoned or directed by a peace officer to make the arrest, except that he or she is justified in the use of force likely to cause death or great bodily harm only when he or she reasonably believes that the force is necessary to prevent death or great bodily harm to himself or herself or another.
(B) A private person who is summoned or directed by a peace officer to assist in making an arrest which is unlawful, is justified in the use of any force which he or she would be justified in using if the arrest were lawful unless he or she knows that the arrest is unlawful.
(ILCS Chapter 720, Act 5, § 7-6) (1981 Code, § 42.07, 7-6)