In the 16th episode of season six, “Broken Bird,” it’s revealed that Ducky, who hails from Scotland, served in the Royal Army Medical Corps, which took him to Afghanistan in 1980. While working in a refugee camp, Ducky met a Polish interrogator working for the CIA named Marcin Jerek, who was nicknamed “Mr. Pain.” Ducky discovered that Jerek had been torturing prisoners. When Jerek would send them to Ducky for care, he would euthanize them with a morphine injection. Finally, Jerek tortured a man he knew to be innocent, Javid, specifically to break Ducky’s compassion for the refugees. Ducky euthanized Javid and regretted it ever since.
Years later, when the episode took place, Javid’s sister attacked Ducky and accused him of violating the Geneva Convention. The Afghan government learned of the incident and planned to investigate Ducky. Then Ducky tracked down Jerek and confronted him, and Jerek finally confessed to his crimes. But Ducky’s role in the tragedy still haunted him for years.