There is thread on this site, in the Real Life Stories section, titled 'Bizarre situation'. http://www.utahconcealedcarry.com/forum/viewtopic.php?t=1176
Scenario's like this, and Many others, always seem to spark a good discussion that deals with Levels of Force, and when a person is Justified in using deadly force.
Years ago I learned about an acronym called AOJP - Ability, Opportunity, Justification, and Preclusion. I later found a link to a web site that does a great job describing what each term means, and why it's important to have good understanding of it, in case you are faced with a possible 'Deadly Force' encounter.
TMG, GREAT Topic. In our CFP classes we talk about "Intent, Opportunity and Capability". I brought this over from my Military days in the Air Force as a cop. I also used the same idea as a civilian LEO.