Heisenberg I believe tried to sabotage the Nazi effort to make an atom bomb. The proof is two fold. One is that in 1939 he was specifically asked to write a paper on the question if a chain reaction with Uranium is feasible, and if so how much Uranium would be needed. His entire paper side swiped the question, and dealt only with the question of using uranium as an energy source. But that is just one half of the issue. Later after the war he was interred with other physicists, and when they heard about the success of the USA is creating a atom bomb, they wondered how much uranium was needed. Heisenberg did not know, but set off to making the calculations. Then in a short time he came up with the right answer. That shows that five years before that when he was asked that exact question by Nazis, he did not even bother making the calculations at all, but on purpose sidelined the entire question. 

[But the Nazis did  have a few other secret bases where they were working on the same idea.]