Jedi Mind Trick
The most murderous organization in the U.S. today is a prison gang called the Aryan Brotherhood (or the Brand). The New Yorker's David Grann wrote about them in a recent issue. It's not on the website, but they do supply a Q&A with Grann:

Part of the reason for the gang’s success is that its members are simply incredibly cunning. The gang selects only the most violent and capable individuals to become "made" members—individuals who are, as one former gang member put it, "master manipulators."

later in the Q&A:

Q: Some prisoners are able to charm women on the outside into helping them. What motivates these women?

A: It is hard to say, precisely. One woman who had no criminal record—and who later stood by as a gang member murdered a deputy sheriff in her presence—claimed that she had Stockholm syndrome. I think that in some cases the women are drug users who are able to get a free supply on the outside from the gang’s contacts. More often, though, I think these are lonely individuals who seem to be seduced by the leaders, just as inmates who come into prison are seduced into killing and stabbing for the gang.

Grann reports an Assistant U.S. Attorney has indicted forty members of the Brand and is seeking the death penalty for twenty-three of them in an effort to cripple the organization.