“Titanic's Ghosts” traces efforts to use DNA technology to identify three victims of the sunken ship whose remains are buried in a Halifax, Nova Scotia, cemetery. The three: a woman in her early 30s, a man in his early 20s and a boy who was about 2. “It would be a rounding off of the whole tragedy,” says an Englishwoman who's hoping that the young man was her uncle. The hour also chronicles the Titanic's sinking, on April 12, 1912; and the recovery of 328 bodies a week later by Canadian sailors. Liev Schreiber narrates.