for the years preceding her death and how she's just being beaten down psychologically and mentally. >> reporter: it took the detective nearly a year and a half to listen to all of the recordings. and by then, he'd heard more than enough. when he learned that matt would be returning to georgia to testify in a civil suit concerning the payout from some life insurance policies nikki had, he planned to be waiting. >> coming up, would investigators have it all wrong? nik nikki's youngest daughters paint a picture of her mother's inner battles. >> she would hear voices. >> and why they are furious with her mom's side of the family. when "dateline extra" continues. i have to tell you something. dad, one second i was driving and then the next... they just didn't stop and then... i'm really sorry. i wrecked the subaru.