Who is Elsa and Dan from Without Conscience: The Disturbing World of the Psychopaths Among Us and what is their importance?

Elsa was "taken in" by Dan. As a traveler in London, Elsa was very lonely. Dan, was attracted to her weakness and loneliness. He charmed her, and started to spend a lot of time with her. Pretty soon, Dan was using Elsa for money and shelter while refusing to answer her questions about his whereabouts and actions. Eventually, Dan blew up at her and moved on.