Helen Alderman was a young girl when she learned that her great-uncle was the Florida soldier executed on July 7, 1865, with three others who had conspired to assassinate President Abraham Lincoln. On a sunny afternoon 129 years after Lewis Thornton Powell’s death, Alderman, 72, and about two dozen friends, family and historians gathered Saturday under the shade of six cypress trees at a Geneva community cemetery to bury a small mahogany box and close the story of the Florida farm boy who joined John Wilkes Booth in one of the most notorious acts in American history. “Never in my...