Death Squads
One of the first and most notorious, called the "Mano Blanca" or the White Hand, was responsible for thousands of killings alone in the late 60's and early 70's. It would serve as a model to human-rights abusing militaries and authoritarian governments across the hemisphere.
In the mid-1960's Guatemala saw the emergence of wide-spread terror and killings at the hands of "death squads". Often these were composed of off-duty police officers or soldiers who acted unofficially on behalf of right-wing political groups and interests.