Mohamedou Ould Slahi and Steve Wood met in Guantanamo Bay, Cuba, in 2004.
At the time, Slahi had been in captivity for two years, accused of acts of terrorism.
Wood, then a member of the National Guard, was assigned to watch the Mauritania native. For nine months, they spent their days together.
After more than a decade, the two saw each other once again this spring, when Wood traveled to Slahi's home in Mauritania to see his old friend.