I've always believed that the TVZ song more or less followed the story of the film "Viva Villa!" (1934; Wallace Beery). There was a reporter named Wallace who was portrayed as a sort of Boswell to Villa. And according to the film Villa was killed by a relative of one of the "wives" he had wronged. I don't recall any hint that the reporter had betrayed Villa in the film, but it's been at least 30 years since I've seen it. Doesn't anyone else here remember it?

For web references:
http://www.geocities.com/cinemorgue2/wallacebeery.html
http://www.imdb.com/title/tt0025948/

Sorry, my blue clickies never work.