The most famous escapee was the Boer prisoner of war Captain Fritz Joubert Duquesne who was serving a life sentence for "conspiracy against the British government and on (the charge of) espionage.". On the night of 25 June 1902, Duquesne slipped out of his tent, worked his way over a barbed-wire fence, swam 1.5 miles (2.4 km) past patrol boats and bright spot lights, through storm-wracked, shark infested waters, using a distant lighthouse for navigation until he arrived ashore on the main island. From there he escaped to the port of St. George's and a week later, he stowed away on a boat heading to Baltimore, Maryland. He settled in the US and later became a spy for Germany in both World Wars. In 1942, Col. Duquesne was arrested by the FBI for leading the Duquesne Spy Ring, which still to this day the largest espionage case in the history of the United States.
What was Captain Joubert Fritz Duquesne serving a sentence for? (If the question is unanswerable, say "unanswerable")
unanswerable