i am not going anywhere, tell me what's happening. >> cheating husbands, scheming wives. suburbs are fill of secrets, but being unfaithful to your spouse isn't a crime, is it? that would come next. >> 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's armed and ready. >> two couples, two families, and the single moment that shattered it all. >> i knew one day that this was all going to come out. hello and welcome to "dateline." it's a cautionary tale that started with two seemingly happy couples in suburban, idaho.