Not uncommon for these muslim fundamentalist types to have criminal histories. Historically those of a criminal bent, psychopaths,sadists, 
and sociopathic types are often drawn to causes where they can act out their criminal tendencies under the cover of a righteous cause.
This was also true for Hitler and his Brown Shirts which later morphed into the SS (Schutzstaffel) and the secret police (Gestapo).
This may explain to some extent why groups such as ISIS, Al Queda, Boko Haram, Hamas, PLO, the Moslem Brotherhood, often employ
extremely cruel, and sadistic  means of killing their victims.  It is the perfect storm for these individuals, they get their jollies while gaining
fame and admirations from their peers.