In the aftermath of the murders that horrified America, family killer Chris Watts became obsessed with controlling the story of what happened inside his suburban Colorado home.

The father-of-two initially lied to police that his pregnant wife Shanann and their daughters Bella, four, and Celeste, three, had simply vanished. Then, when that narrative collapsed, Watts falsely claimed Shanann had killed the girls - and that he murdered her as revenge.

He later admitted to slaughtering his entire family so he could start a new life with his mistress. But from prison, Watts would go on to paint himself as a victim who had been manipulated and led astray by the affair.

According to a woman who spent years in close contact with Watts behind bars, his obsession with controlling the narrative extended beyond his public confessions.

There were, she said, details of the killings he desperately did not want the public to see.

Now, nearly eight years later, the Daily Mail is revisiting grim evidence buried deep in the case files that Watts never wanted fully aired.

They include photographs of the bloodied clothing Shanann was wearing on the night she was murdered, disturbing autopsy findings, and chilling discovery material that paints an even darker picture of crimes that already shocked the nation.

'He didn't want it to get out,' the woman said.

'I think once he realized what he had done, the idea was just too gruesome.'

The source said Watts, now 41, was especially troubled by autopsy findings detailing the injuries suffered by his daughters.

He smothered them and forced their bodies through the narrow hatches of oil tanks at the Anadarko Petroleum site where he worked.

'Think of a dinner plate; he was stuffing the girls through a hole smaller than that,' she said. 'Just really awful.

'If you read the reports, they're horrifying. He didn't want that to be out there, because that makes him look like even more of a monster.'

During the early stages of the case, prosecutors tried to temporarily seal autopsy reports and related graphic materials before the trial, including photographs and forensic evidence.

They said their release could prejudice the jury and reveal key pieces of evidence to the defense. 

But Watts' guilty plea in August 2018 meant there would be no trial.

But according to the female pen pal, Watts privately asked lawyers whether there were ways to keep the records from becoming public even after his confession. 

That effort ultimately failed.

Under Colorado law, autopsy reports are generally considered public records once an investigation is complete unless a judge determines their release would substantially harm the public interest.

And the reports make for grim reading.

Four-year-old Bella Watts was still dressed in a pink pajama-style top decorated with hearts and butterflies when her body was recovered from one of the oil tanks.

By then, the clothing had been drenched in thick black crude oil.

Beneath it, she wore only a pair of oil-soaked underwear.

When pathologists examined her body, they found green-black oily fluid and debris inside her stomach.

The coroner also noted injuries inside Bella's mouth, trauma to her jaw, and bite marks on her tongue, signs of how she fought for her life before she was smothered.

Her three-year-old sister Celeste was found wearing a pink-and-black t-shirt, a diaper and underwear, all saturated in oil and debris from the tank.

Both girls' bodies showed severe decomposition after days submerged inside the containers.

The autopsy described bloating, discoloration, skin slippage and damage to internal organs.

Yet despite the unimaginable condition in which they were found, the official cause of death for both girls was the same: smothering.

The woman who communicated with Watts in prison said the findings shattered any attempt to soften the reality of what happened.

For narcissistic people like Chris, she said, controlling the narrative makes them feel better about themselves. The autopsies left no room for doubt.

Watts claimed he lost control and was possessed by evil on the night of the killings. But chilling details buried in the discovery files suggest they may have been pre-planned.

Just days before the murders, Shanann received a photograph via text from her husband showing a large plastic doll wrapped in a sheet-like fabric.

Watts claimed the girls had done it while playing.

The image would later horrify followers of the case because of its disturbing similarity to the way Shanann's body was discovered, buried in a shallow grave.

Some psychologists describe behavior like this as 'duping delight' - a phenomenon in which deceivers subtly leave clues or breadcrumbs for the thrill.

Meanwhile, photographs from the investigation show the clothing Shanann was wearing when Watts murdered her before dumping her body near the oil site.

The items included a heavily soiled shirt, blue underwear and a black bra recovered from the burial site.

Disturbingly, Watts later claimed in police interviews that he and Shanann had sex on the night of the murders.

Text messages sent by Shanann to friends as the couple's marriage hit the rocks in early August suggest the couple's sex life remained active until around two months before.

That timeline lines up with when Watts is believed to have started his affair with co-worker Nichol Kessinger in the summer of 2018.

Former Watts cellmate Dylan Tallman told the Daily Mail the killer blamed his sudden intense lust for Kessinger for destroying his life.

Tallman said Watts described Kessinger as a 'Jezebel' - a Biblical term often used to describe a manipulative or morally corrupt woman who leads men toward ruin.

'I was having an affair with this girl, and I ended up in love with two women at the same time,' Watts told Tallman, according to the former inmate.

'It's what led up to what happened. She is of evil spirits, like Jezebel.'

Other little-publicized details from the discovery files show how Watts and Kessinger were consumed by the affair in the weeks before the murders.

According to our source, who wrote to and visited Watts in prison, the killer frequently bragged about the intensity of their relationship and claimed they spent hours talking and exchanging explicit messages.

Internet searches later recovered from Kessinger's phone also showed searches for pornography on days she met up with Watts.

Several searches show her looking for 'interracial sex' and 'threesome with double penetration' content before her trysts with Watts.

Nearly eight years later, the horror contained inside the Watts case files show why the murders continue to grip America long after the guilty plea.

They also show why some of the details Chris Watts wanted hidden most remain impossible to forget.

Watts is being held in Wisconsin without the possibility of parole.