Mengele was brought over to the U.S., according to Freedom of Information Act documents, as part of the CIA's Operation Paperclip after WWII, (in which Nazi scientists and Nazi war criminals were brought over to win the technology war against the former Soviet Union.)
The price of Nazi scientists cooperation was the freedom of thousands of Nazi war criminals like Mengele. They sold their services to both sides and incited, even fabricated parts of the Cold War to suit their own ends.
The Nazis co-opted 5000 year old bloodlines in generational occult families seeking to breed persons with abnormally high fertility and supernatural abilities. They also made use of persons in the occult committing the most horrible crimes against children for the stated purpose of creating persons with DID --more commonly known as Multiple Personality Disorder.
These practices are still ongoing. The stated purpose of these crimes both in the former USSR and here in the US was to create the perfect soldier, the perfect spy, and the perfect assassin, persons who with a key word or phrase could be made to do the bidding of their handlers unquestioningly and not remember it later nor be able to disclose classified information even if they wanted to.
They were also interested in remote viewing, divination, and the military applications of a multitude of extrasensory abilities including "red fire" or psychic killing. See Carol Rutz' book "A Nation Betrayed." Programmed messengers and programmed sex slaves were also created for the demented pleasures of the rich and famous.
This program was called MK-ULTRA and involved confiscating super bright children and naturally occurring high order multiples---especially identicals---from their natural parents and putting the children with persons who would allow abuse and experimentation. The program is still ongoing and now uses and manipulates the Child Protection system to facilitate these activities.
Also see Criminals of War and Mengele.dk