WARNING: GRAPHIC CONTENT
Killer dad Chris Watts has revealed chilling details about his pregnant wife's murder in a disturbing bombshell prison letter, according to reports.
In a grisly letter to author Cherlyn Cadle, the 35-year-old gave gruesome details of his wife Shannan's slaying - revealing he had been thinking about killing her for weeks.
In the letter, obtained by the Daily Mail, he wrote: "Her eyes filled with blood; as she looked at me and she died. I knew she was gone when she relieved herself."
Watts is currently serving multiple life sentences for the murders of his wife, who was pregnant with the couple's son Nico, and his two daughters Bella,4, and Celeste, 3.
He also confessed that he had slipped the potent painkiller Oxycodone to his wife in the hope of inducing a miscarriage, in the hope of eventually moving on with his co-worker Nichol Kessinger who he had an affair with.
"I thought it would be easier to be with Nichol if Shanann wasn't pregnant," he wrote.
Describing her death, Watts wrote: "When she started to get drowsy, I somehow knew how to squeeze the jugular veins until it cut off the blood flow to her brain, and she passed out.
"I knew if I took my hands off of her, she would still keep me from Nikki. They asked me why she couldn't fight back, it's because she couldn't fight back.
"All the weeks of me thinking about killing her, and now I was faced with it."
In letters to Cadle, he admitted he unsuccessfully tried to smother their young daughters after an argument with his wife.
He said they both regained consciousness after initially thinking they were dead.
Watts revealed his daughters got out of bed bruised and traumatised after he killed their mother.
Watts said he knew he would kill them but "did nothing to stop it" and felt "mad" when he discovered they were still alive after his murder attempt the next day.
The terrified children found Watts wrapping their mum in a bed sheet, the letter said.
Watts said he told them Shanann wasn't feeling well before dragging her lifeless body down the stairs and into his truck.
He then drove Shannan's lifeless body and his two frightened daughters to an oil field.
Watts then killed Celeste before squeezing her body through an eight-inch hatch in one of the oil tankers.
He then killed Bella after she watched him kill her sister.
"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."
Shanann's cause of death was strangulation while an autopsy found crude oil in Bella and Celeste's throats, stomach and lungs.
Watts previously told investigators that Shanann's killing was a spur-of-the-moment crime of passion and didn't admit to planning it.
The letter is the first time he's acknowledged killing his kids.
Watts later pleaded guilty to all three killings and his mistress Kessinger has been taken into witness protection in another state.