1.) The Nazi Party
2.) He was charged with crimes against humanity.
3.) He was an SS physician whose research was aimed at helping populate Germany after the war (assuming a Nazi victory). He wanted to ensure that there were enough Aryans to fill the "liebenstrom", or "living space" that Hitler had conquered. He also oversaw the administration of Zyklon B, the gas used in the chambers. He would also perform hospital checks, and anyone who had not recovered after two weeks was immediately sent to the gas chambers.
4.) He was nicknamed the Angel of Death, due to the brutality and inhumanity of his experiments.
5.) Mengele was the one who prisoners would pass before in a line. Mengele would either point left or right. Those going left were immediately sent to the gas chambers. Those going right would live another day.
6.) His research was mainly in the area of genetics and heredity. He wanted to prove the idea of heredity over environment, which would strengthen the Nazi ideology. He had a particular interest in twins. He was interested in finding out if there were ways to increase the chances of Aryan women having more children, so populating the liebenstrom would be easier.
7.) He suffered a stroke while swimming and drowned
8.) Same as number two