Other mistake: The 30 second timer counting down in the garage trap actually takes 87 seconds to count down. The first 17 seconds take 72 seconds to pass. (00:20:15)
Other mistake: When Suzanne is in the trap there is one point where we see 36 seconds remaining on the clock. If you listen carefully you can continue to hear the clock tick down once per second, even offscreen, and you can count about 45 ticks before Suzanne is killed. (00:44:45)
Other mistake: Bobby extracts 2 teeth forcibly to get into the final room, however when he's in the other room his mouth is no longer bleeding. The blood wouldn't stop that quickly. (01:02:15 - 01:10:00)
Answer: He, his wife and his daughter were abducted before he decided to work with Jigsaw. He didn't put them in danger. As for why he decided to work with Jigsaw following his ordeal, like other characters in the franchise, he either developed a level of Stockholm syndrome or he concluded that Jigsaw's methods were right, or a combination of both.
Phaneron ★