[Aguila Blanca]

Are you certain that you don't have a castle doctrine? That would surprise me very much.

[edit to add]

13 V.S.A. § 2305. Justifiable homicide

§ 2305. Justifiable homicide

If a person kills or wounds another under any of the circumstances enumerated below, he or she shall be guiltless:

(1) In the just and necessary defense of his or her own life or the life of his or her husband, wife, parent, child, brother, sister, master, mistress, servant, guardian or ward; or

(2) In the suppression of a person attempting to commit murder, sexual assault, aggravated sexual assault, burglary or robbery, with force or violence; or

(3) In the case of a civil officer; or a military officer or private soldier when lawfully called out to suppress riot or rebellion, or to prevent or suppress invasion, or to assist in serving legal process, in suppressing opposition against him or her in the just and necessary discharge of his or her duty. (Amended 1983, No. 23, § 2.)

That's a start. Not strictly a "castle doctrine" law, but fairly wide in scope. I'd say #2 fits the incident pretty well. The robber had a knife -- a deadly weapon. The clerk "suppressed" the robber.