I. A law enforcement officer is justified in using non-deadly force upon another person when and to the extent that he reasonably believes it necessary to effect an arrest or detention or to prevent the escape from custody of an arrested or detained person, unless he knows that the arrest or detention is illegal, or to defend himself or a third person from what he reasonably believes to be the imminent use of non-deadly force encountered while attempting to effect such an arrest or detention or while seeking to prevent such an escape.
II. A law enforcement officer is justified in using deadly force only when he reasonably believes such force is necessary:
(a) To defend himself or a third person from what he reasonably believes is the imminent use of deadly force; or