[cobra de capell]

The movie implied that one of them couldn't quite accept the rape of the little girl

Apparently, but not shown or implied - the interest in the 'girl' angered one con in that he was being thrown over for a 'girl.' That's why the family was killed as outlined within the blog. Just hanging around simply doesn't come up with sufficient motive to kill everyone. Capote was fluity. For some reason, he elected not to tell the story with the fruity element attached even with it being huge as to why the family was killed.