Criminal Law Capsule Summary

§ 9.01 Common Law Rule

Generally speaking, a person is justified in using force to protect a third party from unlawful use of force by an aggressor to the extent that the third party is justified in acting in self-defense. This so-called "alter ego" rule, as applied in early common law, required that the third party had to in fact have been justified in self-defense, irrespective of how the situation would have appeared to a reasonable person. Today, however, the majority view is that the use force may be justified if it reasonably appears necessary for the protection of the third party.

§ 9.02 Model Penal Code

[A] General Rule – Subject to retreat provisions, Section 3.05(1) justified force by an intervenor in order to protect a third party if:

	1.)	he uses no more force to protect the third-party than he would be entitled to use in self-protection, based on the circumstances as he believes them to be;
	2.)	under the circumstances as he believes them to be, the third party would be justified in using such force in self-defense; and
	3.)	he believes that intervention is necessary for the third party’s protection.

[B] Effect of Retreat Rules – The Code’s retreat rules have applicability in very limited circumstance here:

	1.)	the intervenor is only required to retreat before using force in protection of a third party in the unlikely circumstance that he knows that such retreat will assure the third party’s complete safety. [MPC § 3.05(2)(a)]
	2.)	the intervenor must attempt to secure the third party’s retreat if the third party herself would be required to retreat, if the defendant knows that the third party can reach complete safety by retreating. [MPC § 3.05(2)(b)]
	3.)	neither the intervenor nor the third party is required to retreat in the other’s dwelling or place of work to any greater extent than in her own dwelling or place of work. [MPC § 3.05(2)(c)]