just tell me what is happening. >> cheating husbands and scheming wives, suburbs full of secrets. but being unfaithful to your spouse is not a crime, is it? that would come next. >> oh, my god! >> it was just like every emotion possible all in one second. >> i went, oh, my god. >> murder in the dark. who was behind it and who would pay. >> when you see him on the video, he is armed and ready. >> two covers, two families and if single moment that shattered it all. >> i knew one day, that this was going to all come out. hello, and welcome to "dateline," it's a cautionary tail that started with two seemingly happen couples in suburban idaho and then it ended