Simplify the following text for a Grade 16 native English-speaking person.
Original: Himmler was responsible for establishing and operating concentration camps and extermination camps in which millions of inmates died of systematic mass gassing , shooting , hanging , inhumane treatment , overwork , malnutrition , or medical experiments .
Simplified: The SS was responsible for establishing and operating concentration camps and extermination camps in which millions of inmates died of inhumane treatment , exploitation , malnutrition or medical experiments .