I only have information on one, and that's [loosely translated] the Baghdad SWAT. Of course, since Iraq never attended the Geneva conventions, they handle everything that Allied forces can't. Each squad is equipped with one torturer to garner 'assured success in every mission'.
the Baghdad SWAT also specialize in night-time sorties, which will empty entire city blocks house-by-house, and kill anyone who doesn't cooperate.
the local returners who I interviewed all had the same views "What they do ain't anything America should be doing. "
Give me a moment, and I'll gather some info on the Viet Nam/Guam mercenary groups.