Captain Witold Pilecki of the Polish Home Army conceived and executed what may be the most courageous intelligence operation in history. In September 1940, he intentionally got himself arrested during a German street round-up in Warsaw, using a fake identity, to be sent to Auschwitz.
Inside the camp, Pilecki organized a resistance network called the Union of Military Organizations (ZOW), built a radio transmitter from stolen parts, and compiled detailed reports about camp conditions and the systematic extermination of prisoners. His reports, smuggled out to the Polish underground and forwarded to the British, were among the earliest complete accounts of the Holocaust—but were largely disbelieved as too horrific to be true.
After nearly three years, Pilecki escaped Auschwitz in April 1943 by overpowering a bakery door guard during a night shift. He continued fighting in the Polish resistance, taking part in the Warsaw Uprising of 1944. Tragically, after the war, the Soviet-installed communist government arrested him on fabricated charges of espionage. He was tortured and executed in 1948. He was not officially rehabilitated until 1990.