Why didn't Kerrest take his own gun...

I generally enjoyed the movie and was entertained, even though I narrowed it down pretty early to Kerrest or Lanyon as the killer. Too bad the ending had some serious defects.

Why didn't Kerrest take his own gun back from Anna and cover Lanyon while ordering him to drop the gun? Why walk over to Lanyon and ask him nicely to give it up? What policeman would ever do something so stupid? And how could Lanyon, who was mortally wounded by Anna, overcome Kerrest, a larger man, when fighting him for control of Lanyon's gun? These are rhetorical questions; the answers are: 1. he would have, 2. he wouldn't, 3. no policeman would, and 4. he almost certainly couldn't.

Also, it's way too convenient that Kerrest grew up on the island (to which he naturally took Anna to hide) with very few people and a tiny school that are the perfect places for her to live and teach - now that the "105 year old" teacher retired just in time for Anna's transfer.