Question I have asked myself after reading the German wikipedia biography of Josef Mengele, who continued to defend his actions on Nazi ideology until his death in 1979, once even claiming he has never killed someone. Of the major war criminals at Nuremberg, only Albert Speer seems to have taken some moral responsibility, yet he actively obscured his involvement namely in the holocaust in all of his later books. So, does anyone know someone who truly confessed and accepted his guilt?
There is the borderline case of Rudolf Hoess (or Hoss with the umlat thing), commandant of Auschwitz
https://www.shu.edu/academics/theology/upload/mass-murderer-repents.pdf
The 'borderline' is as you'll read it's not like it was a total about face, that by the end he completely turned on the Nazi ideology and Hitler
Noteworthy in Hoess's final declaration is the absence of any reference to Jews. Repentance, especially for crimes as grave as those of Rudolf Hoess, is a process, seldom a single act. Hoess started on the road of repentance. He did not finish the journey. Those who would withhold recognition because his repentance was incomplete would do well to reflect that few, if any, of Hoess's colleagues expressed any regret for their crimes at all.
just to get a bit more information for someone who isn't as ignorant as I: Do you mean people who committed actual war crimes and now feel guilty or people in the Nazi party and regretted being associated with it?
The answer could be Doenitz, with a bit of a caveat. He ended up condemning nazism and fascism as deeply flawed systems of government. Saying that much of the true evils of the war were to be attributed to the inequities inherent to the system of government. He had been a firm believer in both Hitler and the NSDAP during the war. Notably, he had been a huge fan of the Hitler Youth, earning the nickname Hitlerjugend Doenitz.
He changed in the post war years, regretting that he hadn't helped Speer steer Hitler away from his burnt earth policy in the east or that he hadn't protested the gradual growth of the SS. But... He couldn't extricate himself from his quite quotable nazi era antisemitism. He muddled his record further by arguing for an unapologetic militarist view of his and other officers records. He believed that the military had had and still required complete obeisance to the state during times of war which his critics would use to further the view that he was an opportunist rather than a true repentant.
So, he may or may not be the answer. He was clearly repentant about nazism and fascism but he can be said to have been clearly unrepentant about the way he conducted himself during the war. Since he even served as Führer for a short time, there really isn't anyone higher than him that showed any kind of contrition.
Sourced mainly from Doenitz's memoires.