SS(Schutzstaffel, Protection Squad), originally Adolf Hitler's bodyguard, it became the elite guard of the Nazi state and its main tool of terror. The SS maintained control over the concentration camp system and was instrumental in the mass shootings conducted by the Einsatzgruppen.
Led by Heinrich Himmler, its members had to submit with complete obedience to the authority of the supreme master, Hitler and himself. SS officers had to prove their own and their wives' racial purity back to the year 1700, and membership was conditional on Aryan appearance.
In the charter of the International Military Tribunal at Nuremberg (commonly known as the Nuremberg War Crimes Trials) the SS was held to be a criminal organization. Its members were considered war criminals involved in brutalities and killings in the concentration camps, mass shootings in the occupied countries, involvement in the slave labor program and the murder of prisoners-of-war.
Source: Encyclopedia of the Holocaust.