of "dateline." i'm craig melvin. thank you for watching. >>> i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." >> you had the good cop. you had the bad cop and the polygraph. it felt like "law and order." >> the fire broke out before dawn. in the daylight they found this mother is of two young children dead. >> she lived a very courageous life. she was very bold in the things she did. >> after the smoke cleared, a priss tree lingered. >> we knew she did not die in that fire. she died before the fire. >> who do you look to as the suspect? >> obviously the spouse is the first person you look to. >> but her husband had a clear alibi, and he passed a lie detector test. eventually the case grew cold until this witness came forward with a tale of love and lust gone wrong.