Meanwhile, Lawrence's wife and daughter, Alison and Diana, are being held captive in their home by a man who is watching Adam and Lawrence through a camera behind the bathroom's mirror while tormenting Alison and Diana. Their house is simultaneously being watched by Tapp, who was discharged from the force. Flashbacks show that he became obsessed with the Jigsaw case after viewing Amanda's testimony, and that he and Sing illegally entered a warehouse they knew to be Jigsaw's lair and saved a man from being killed by drills aimed at his neck. Jigsaw managed to make a run for it after slashing Tapp's throat, and Sing was killed by a shotgun booby trap while pursuing him. After being discharged, Tapp began stalking Lawrence.
In the bathroom, Lawrence finds a cigarette, a lighter, and a mobile phone that can receive calls but not send them. He and Adam use the first two items to try to stage Adam's death, but an electric shock through Adam's ankle chain foils this plan. Following these events, Adam and Lawrence recall their abductions; they were both ambushed and knocked unconscious by a stranger wearing a gruesome pig mask. Lawrence receives a call from Alison, who warns him that Adam knows more than he is telling. Adam explains that he was paid to take pictures of Lawrence for the past few days by Tapp, and shows Lawrence a pile of pictures of him from the bag containing the hacksaws. Lawrence berates Adam for invading his privacy, while Adam shows Lawrence evidence that he was cheating on Alison. Adam then notices a picture of a man in Lawrence's house; Lawrence identifies the man as Zep Hindle, and the two deduce that Zep is their abductor. Adam then points out that it is six o'clock, the deadline. Zep moves to kill Alison, but she frees herself and manages to overpower Zep, gaining Tapp's attention in the process. He arrives in time to save Alison and Diana from Zep, allowing them to escape. Zep then flees to the sewers with Tapp in pursuit.
Lawrence, who is only aware of gunshots and screaming, is zapped by the ankle chain as well and loses reach of the phone; in desperation, he saws off his foot and shoots Adam with the corpse's revolver. Zep, who shot Tapp during the chase, enters the bathroom intent on killing Lawrence, only to be blindsided by Adam (whose shoulder wound had not been fatal) and beaten to death with a toilet tank cover. As Lawrence crawls away with the promise that he'll return with help, Adam searches Zep's body for a key and finds another microcassette recorder. He learns that Zep was another victim of the game, following rules to obtain an antidote for the slow poison within his body. In the film's iconic ending, the corpse in the middle of the room rises to its feet and reveals itself as John Kramer, the real Jigsaw Killer. He tells Adam that the chain's key is in the bathtub, which was drained when Adam accidentally kicked the plug out. Adam grabs Zep's pistol and tries to shoot Jigsaw but is electrically shocked by his hidden remote control before he can do so. Jigsaw then turns off the lights and seals the door to the bathroom, leaving Adam to die.