563.051. 1. A private person who has been directed by a person he reasonably believes to be a law enforcement officer to assist such officer to effect an arrest or to prevent escape from custody may, subject to the limitations of subsection 3, use physical force when and to the extent that he reasonably believes such to be necessary to carry out such officer's direction unless he knows or believes that the arrest or prospective arrest is not or was not authorized.
2. A private person acting on his own account may, subject to the limitations of subsection 3, use physical force to effect arrest or prevent escape only when and to the extent such is immediately necessary to effect the arrest, or to prevent escape from custody, of a person whom he reasonably believes to have committed a crime and who in fact has committed such crime.
3. A private person in effecting an arrest or in preventing escape from custody is justified in using deadly force only
(1) When such is authorized under other sections of this chapter; or
(2) When he reasonably believes such to be authorized under the circumstances and he is directed or authorized by a law enforcement officer to use deadly force; or
(3) When he reasonably believes such use of deadly force is immediately necessary to effect the arrest of a person who at that time and in his presence
(a) Committed or attempted to commit a class A felony or murder; or
(b) Is attempting to escape by use of a deadly weapon.
4. The defendant shall have the burden of injecting the issue of justification under this section.
(L. 1977 S.B. 60)
Missouri General Assembly