"Oskar Schindler: Stepping Stone to Life" by Robin O'Neil
"Oskar Schindler's exceptional deeds stemmed from just that elementary sense of decency and humanity that our sophisticated age seldom sincerely believes in. A repentant opportunist saw the light and rebelled against the sadism and vile criminality all around him. The inference may be disappointingly simple, especially for all amateur psychoanalysts who would prefer the deeper and more mysterious motive that may, it is true, still lie unprobed and unappreciated."--Robin O'Neil
Oscar Schindler was an ethnic German citizen of Czechoslovakia who joined the separatist Sudeten German Party in 1935.
I have read Thomas Keneally's famous novel Schindler's List, but a former Scotland Yard detective turned scholar named Robin O'Neil [Wikipedia] has written a facinating on-line account of Oskar Schindler's [Wikipedia] transformation from an opportunist and even spy for the German military intelligence, the Abwehr, into a humanitarian hero who saved over 1000 Jews from Hitler's gas chambers.
The head of the Abwehr, Admiral William Canaris, was also initially a supporter of Hitler who had a change of heart when he realized that Hitler's policies would bring ruin to Germany. Canaris was executed for his alleged involvement in the 20 July Plot to kill Hitler. O'Neil's interesting book is titled Oscar Schindler: Stepping Stone to Life. Click the title to see the book on-line.