My understanding from the Wikipedia is that Nazario Moreno was a Catholic (which almost all Mexicans were until not too long ago), that he converted and became a witness, and that he later left the Watchtower to create a cult-like drug organization. He used a book to indoctrinate others.
This was published in a Mexican newspaper (http://www.vanguardia.com.mx/nazariomorenogonzalezeladoctrinador-606663.html): Nazario Moreno González, the indoctrinator.
El Chayo se dedicaba a motivar psicológicamente a sus huestes. La PGR encontró en un cateo lo que los fiscales llaman "la biblia" de ese grupo criminal, supuestamente escrito por él.
"Chayo" was in charge of psychologically encouraging his solders. During a search, The Office of the Prosecutor General found what prosecutors call "The Bible" of that criminal group, allegedly written by [Nazario Moreno].
So, he was not a practicing Jehovah's witness and he was not a member in good standing. The Watchtower isn't guilty of what he personally chose to do. He could have chosen to stay as a rank-and-file member, but chose violence instead, and found the death he had himself inflicted on others. No pity for the man here. La Familia usually beheads his enemies.
That said, I wouldn't want us to miss the fact that he was an indoctrinator. La Familia Michoacana is the most violent drug cartel in Mexico (which is not to say little), and Nazario Moreno's ability to indoctrinate he got from the Watchtower. So I would say that, while this releases the Watchtower of any responsibility in what the man did, it does give us a reason to try to fight cultic movements wherever they are. Not only do they cause harm, they also spawn harm.
Apparently he made his followers read John Eldredge's books (http://www.jornada.unam.mx/2010/12/11/index.php?section=politica&article=006n1pol).