Cause of death: gangrene
Allan Pinkerton (August 21, 1819 – July 1, 1884) was a Scottish-American cooper, abolitionist, detective, and spy, best known for creating the Pinkerton National Detective Agency in the United States and his claim to have foiled a plot in 1861 to assassinate president-elect Abraham Lincoln. During the Civil War, he provided the Union Army – specifically General George B. McClellan of the Army of the Potomac – with military intelligence, including extremely inaccurate enemy troop strength numbers. After the war, his agents played a significant role as strikebreakers – in particular during the Great Railroad Strike of 1877 – a role that Pinkerton men would continue to play after the death of their founder.
Source : Wikipedia