Chris Watts made harrowing comments about murder of wife and kids in letters he wrote in prison

Warning: This article contains details which some readers may find distressing.

The harrowing details in which Chris Watts recalled murdering his pregnant wife and young daughters were revealed in letters to a former pen pal.

In August 2018 Watts murdered his wife Shannan and their two young daughters Bella and Celeste, known as 'Cece', before dumping their bodies at an oil storage facility.

He was later arrested and pleaded guilty to the murders, receiving life in prison without the possibility of parole for killing Shannan, Bella, Celeste and their unborn son Nico.

Watts' crimes have since been covered extensively in the media, with Netflix creating the documentary American Murder: The Family Next Door which detailed the case.

The case was also covered in a 2019 book by author Cheryln Cadle, who published Letters from Christopher: The Tragic Confessions of the Watts Family Murders after exchanging letters and visiting him in prison.

Cadle's correspondence with Watts revealed harrowing details about the 40-year-old's decision to murder his wife and children, including the fact that he'd been 'thinking about killing' his family for a number of weeks before going through with the horrific acts.

In one letter particularly harrowing letter, Watts recalled watching his wife's eyes fill with blood and mascara streaking down her face as he strangled her to death. "Isn't it weird how I look back and what I remember so much is her face getting all black with streaks of mascara," he wrote to Cadle.

"All the weeks of me thinking about killing her, and now I was faced with it."

Watts killed his pregnant wife and two young daughters after having an affair with a coworker (Instagram)

Watts also revealed that he'd attempted to smoother daughters Bella and Cece with a pillow before killing Shannan, writing that his daughters 'woke back up' after Shannan died.

"I'm not sure how they woke back up, but they did. Bella's eyes were bruised and both girls looked like they had been through trauma," he wrote.

"That made the act that much worse knowing I went to their rooms first and knowing I still took their lives at the location of the batteries."

He then went on to write that Bella and Cece had walked into the room while he was preparing to dispose of Shannan's body, watching with 'scared looks on their faces'.

"I realise now the girls getting up and walking around may have been God's third attempt to stop what I was doing," he wrote, adding that he'd been ''so mad they were still alive' at the time.

He then drove Shannan's body and the girls, who were both alive at that point, to the oil field. It was here that he buried his wife's body in a shallow grave before smothering the girls and leaving their bodies in crude oil tanks.

He later confessed to the killings and will never be released from prison (RJ Sangosti/The Denver Post via Getty Images)

Watts also wrote about the affair he'd been having with co-worker Nichol Kessinger at the time, whom he'd wanted to start a new life with after killing his family.

"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," he added.