Philadelphia's Eastern State Penitentiary is said to be the one of the most haunted places in America. Since its closing in 1971, many have reported hearing eerie voices, weeping and tormented screams, while others have seen shadows dart in and out of cells. Investigators use the latest technology to search for paranormal activity. Motion sensors are rigged, night-vision and infrared cameras positioned, acoustic triangulation systems set up, and 3-D laser scanners offer a rare view inside.