A dad has confessed to killing his wife and daughters in a haunting letter written in his prison cell.
Chris Watts, 34, admitted his crimes in a letter penned from jail, following his imprisonment for murdering Bella, four, Celeste, three, and his pregnant spouse Shanann.
The convict revealed he drugged his wife in a bid to induce a miscarriage and eventually throttled her to death so he could start a new life with his mistress Nichol Kessinger.
He also said he killed his two girls at an oil field after his first attempt to smother them to death with a pillow failed.
In one of the letters Watts sent to Cheryln Cadle, a stranger he started corresponding with from prison, he wrote: "August 13th, morning of.... I went to Bella's room, then Cece's room and used a pillow from their bed (to kill them).
"That's why the cause of death was smothering. After I left Cece's room, then I climbed back in bed with Shanann and our argument ensued."
Watts failed to tell either police officers or the FBI about the episode when they interviewed him over the murders at his home in Frederick, Colorado, in August 2018.
The murderer also told Ms Cadle he knew he was going to kill his girls the day before he smothered them.
He wrote: "August 12th when I finished putting the girls to bed, I walked away and said 'that's the last time I'm going to be tucking my babies in'.
The killer said his wife's face turn black with streaks of mascara as he told her he no longer lover her before strangling her to death.
He added that she was unable to fight back, describing how she became drowsy and then died while looking at him.
Watts claims his daughters subsequently got out of their beds and caught him wrapping his wife's body in a bed sheet.
He then drove them to a remote oil field, where he killed the two girls and disposed of their bodies, along with his wife's.
The convict wrote: "Out of all three, Bella is the only one that put up a fight. I will hear her soft little voice for the rest of my life, saying, 'Daddy, NO!!!' She knew what I was doing to her. She may not have understood death, but she knew I was killing her."
Watts has allowed Ms Cadle to publish his letters in her book, Letters From Christopher: The Tragic Confessions of the Watts Family Murders, on the condition that she lets people know about his supposed religious awakening in prison.
