What do Robicheaux and Purcel find out about the two brothers in Chapter 6?

Dave Robicheaux and Clete Purcel meet with a prostitute named Ruby Gravano. Ruby tells them about two "johns" who might have been policemen. IRobicheaux and Purcel think they are connected with the murders of the two white brothers and Ruby tells Robicheaux that one of the men had mug shots in his shirt pocket.