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DRY TORTUGAS NATIONAL PARK, Florida Keys — The descendants of a man imprisoned for conspiracy in President Abraham Lincoln’s assassination visited a Florida fortress while fighting for his innocence.

That’s why 80 of them descended on the fort, 68 miles west of Key West, on Friday, the 150th anniversary of Mudd’s July 24, 1865, arrival at the isolated outpost.

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Wearing colorful Key-lime-green “Free Dr. Mudd” T-shirts, they toured Fort Jefferson, a former Union military prison in remote Dry Tortugas National Park, and even viewed a cell where Samuel Mudd spent four years.

Descendants of Dr. Samuel A. Mudd walk into Fort Jefferson in Dry Tortugas National Park, Fla., Friday, July 24, 2015, to mark the 150th anniversary of Mudd's July 24, 1865, arrival at the isolated Gulf of Mexico fort where he was imprisoned after splinting the broken leg of President Abraham Lincoln's assassin. The former Union military prison lies 68 miles west of Key West, Fla. After serving four years in the prison, Mudd was pardoned, but repeated attempts by family members to have his conviction expunged have failed.  (Andy Newman/Florida Keys News Bureau/HO)

Descendants of Dr. Samuel A. Mudd walk into Fort Jefferson in Dry Tortugas National Park, Fla., Friday, July 24, 2015, to mark the 150th anniversary of Mudd’s July 24, 1865, arrival at the isolated Gulf of Mexico fort where he was imprisoned after splinting the broken leg of President Abraham Lincoln’s assassin. The former Union military prison lies 68 miles west of Key West, Fla. After serving four years in the prison, Mudd was pardoned, but repeated attempts by family members to have his conviction expunged have failed. (Andy Newman/Florida Keys News Bureau/HO)

Mudd was convicted and imprisoned after treating the broken leg of Lincoln’s assassin, John Wilkes Booth. But great-grandson Tom Mudd, who spearheaded the family journey to Fort Jefferson, believes the doctor was unaware of Booth’s crime when he splinted his leg.

“History is not cut in stone,” said Tom Mudd during the fort visit. “History is flexible, it’s pliable — and we sincerely believe that Dr. Samuel Mudd was innocent. That’s why we’re here today.”

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Samuel Mudd left Fort Jefferson — called the Gibraltar of the Gulf and believed to be one of the largest masonry structures in the Western Hemisphere — after being granted a pardon in 1869, primarily because of the medical work he did in stemming the spread of a yellow fever outbreak at the fort. But his conviction was never overturned.

This aerial photo shows Fort Jefferson in Dry Tortugas National Park Friday, July 24, 2015. The former Union military prison's most famous prisoner was Dr. Samuel A. Mudd, who was imprisoned for four year after being convicted of conspiring with John Wilkes Booth to assassinate President Abraham Lincoln. On Friday, about 80 of Mudd's descendants made the pilgrimage to the isolated Gulf of Mexico fort  that lies 68 miles west of Key West, Fla., to mark the 150th anniversary of Mudd's July 24, 1865, arrival. Although he was pardoned and released some four years later, family efforts to have his conviction expunged have failed. (Andy Newman/Florida Keys News Bureau/HO)

This aerial photo shows Fort Jefferson in Dry Tortugas National Park Friday, July 24, 2015. The former Union military prison’s most famous prisoner was Dr. Samuel A. Mudd, who was imprisoned for four year after being convicted of conspiring with John Wilkes Booth to assassinate President Abraham Lincoln. On Friday, about 80 of Mudd’s descendants made the pilgrimage to the isolated Gulf of Mexico fort that lies 68 miles west of Key West, Fla., to mark the 150th anniversary of Mudd’s July 24, 1865, arrival. Although he was pardoned and released some four years later, family efforts to have his conviction expunged have failed. (Andy Newman/Florida Keys News Bureau/HO)

Tom Mudd, his father Richard Mudd and other family members have spent nearly 100 years trying to clear their ancestor’s name without success.

“Dad was 102 years old when he said, ‘Tom, we’re never going to win this judicially, but again, in the court of public opinion, we can keep trying — and as long as there is a Mudd alive, we’re going to continue,'” quoted Tom Mudd.

The seven tiny islands that make up the Dry Tortugas, including Garden Key where the fort stands, were designated Dry Tortugas National Park in 1992.

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broadcast, rewritten, or redistributed. The Florida Keys News Bureau contributed to this report.)