Just days after President Lincoln was shot, a lesser-known tragedy unfolded on the Potomac River. In the early morning of April 24, 1865, a military transport steamer, the Massachusetts, accidentally collided with the barge Black Diamond, which had been stationed to help block the escape route of Lincoln’s assassin, John Wilkes Booth. The crash killed 87 people—many of them recently freed Union prisoners of war and four civilian Quartermaster Department employees from Alexandria. Their names—Peter Carroll, Samuel Gosnell, George Huntington, and Christopher Farley—are remembered today at Alexandria National Cemetery.