This ghoulishly intriguing "Nova" episode travels to Ireland's peat bogs to probe two ritualistic killings committed more than 2,000 years ago. The well-preserved corpses (called bog bodies) offer an array of clues from their injuries, which include knife wounds, crushed craniums and dismembered limbs. Experts wield a variety of forensic weapons -- from radiocarbon dating to paleodietary analysis -- to determine how the victims lived and died.