Open this photo in gallery: A man holds an Israeli flag and a sign during a vigil organized by the Jewish Federation of Greater Vancouver in support of those killed in Israel, in Vancouver, on Oct. 10.DARRYL DYCK/The Canadian Press Russ Klein returned from the Thanksgiving long weekend to an outpouring of grief at Vancouver’s King David High School, a private Jewish school where he is principal. The school had just learned that an alumnus, Ben Mizrachi, had been killed by Hamas fighters when a rave he was attending was swept up in the militant Islamist group’s attack on southern...