He was sitting poolside at a resort when an US agent came up to him and said essentially “we found you, we also know where your family is. You can come with us and we’ll get you and your family out, or, you can wait for the Russians to find you, which won’t be long, and you can see what they do with you. The choice is yours, but make it right now.” So he went to the US because he felt his fate was better there. And he wasn’t just a scientist who was being used by the Nazis, he was a hardened nazi. He ran factories with slave labor that had executed corpses hanging from the ceiling. The workers had to go down a hallway to check into work where the bodies of sabotauers were on display and they had to punch them on their way onto the floor. He wasn’t just complicit in that and how things were run, those were his decisions. (I did a humongous project on the V-2 rocket when I was younger. Would have won the national competition in DC if I would have just answered one question the judges were essentially begging me to answer)