Chris Watts killed his wife and two children, then went to an oil field where he buried Shanann in a shallow grave and put the bodies of the girls in oil tanks. Photo / via Instagram

His colleagues called him "silver fox", or "rain man" for his encyclopaedic knowledge of the oil and gas sites where they worked.

No one realised Chris Watts was capable of callously murdering his pregnant wife and children and dumping their bodies in oil drums and a shallow grave.

As the 33-year-old begins his prison sentence, friends and relatives of the killer are picking over the pieces as they try to understand his sickening crime.

The police files paint a heartbreaking picture of how Watts's wife Shanann, 34, panicked as he suddenly turned cold on her and their daughters, Bella, 4, and Celeste, 3.

Watts, who had started an affair with a co-worker, told Shanann they were "not compatible", he had fallen out of love and he resented her need for organisation and control.

"Shanann wanted to change to help her marriage," friends told police. "She wanted to work on that."

'I DON'T KNOW WHO HE IS'

But it was already too late. Watts was making plans to move to an apartment, exchanging explicit photos with his new girlfriend and had told her he loved her.

The affair with Nichol Kessinger, 30, began around the time he learnt his wife was pregnant in June. Almost immediately, his wife noticed something had changed.

As their marriage hit the rocks, Shanann left their home in Denver, Colorado, to visit friends and family in the couple's home state, North Carolina.

When he came to join her and the girls, she told friends, he was a different man. "I don't know where my head is at," he told her.

He would not have sex with her, and when she took his hand during an ultrasound, he didn't hold it back. "He has changed," she wrote, in a chillingly prophetic text. "I don't know who he is."

While she was gone, Watts spent time wining and dining Nichol, longing to start a new life with her. By the time the 33-year-old joined his family in North Carolina after five weeks, he was cold and distant.

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The pair fought and Shanann confided in friends that Watts would not touch or hold her. She had also clashed with his parents over how to raise the girls.

Shanann was distraught, as he rejected her suggestions of marriage counselling and said they were not "compatible".

WEB OF LIES

Before she left for a weekend work trip in Arizona for her sales job, Shanann told friends he had given her signs there might be a resolution. But on the Saturday night, she noticed a credit card bill for $60 from a restaurant.

She contacted Watts to ask what he was doing, her colleagues told police, and he told her he had bought salmon and a beer while out to see a game with friends. The doubtful group of friends looked up the price of that meal at the restaurant in question — it was a third of what he had paid.

He was out with his mistress, while a babysitter cared for the children.

The following night, Nichol spoke to Watts between 9pm and 11pm, and was surprised to hear he was watching television — "odd behaviour for him" because of his 6am start at work. They regularly spoke while he stayed in the basement of the family home, but she recalled wondering if he was waiting up for his wife.

Shanann was dropped off at home by her friend Nickole Atkinson just before 2am on Monday, August 13, and it's at this point that there's a gap in the timeline.

Footage from 5.30am shows Watts backing his work truck up to the garage before driving off, something the family's friends agreed was unusual.

Police believe that at some point during this window he viciously killed his wife and children, before driving the bodies to the site of the oil and gas company where he worked.

'HE DID NOT SEEM OVERLY CONCERNED'

A fellow Anadarko Petroleum employee said she saw Watts digging a hole near an oil drum at the work site.

Nickole, the colleague who had dropped Shanann at home from the airport, knew her pregnant friend had been feeling ill and was concerned when she failed to answer messages and missed a doctor's appointment.

Nicki went to the house, and when she found it empty, she called Watts. He headed home, and by the time he arrived she had called the police.

His behaviour immediately aroused suspicion, with one police report describing his demeanour as "nonchalant".

The officer wrote: "He asked one time if he should go look for his family. I advised him her car was at the residence and I needed him there for now. He did not ask again about looking and he did not seem overly concerned."

Police said his posture was tense, his arms folded and he showed no emotion, glancing nervously around the room. He did not ask any questions or offer to help and his facial expressions rarely changed, except to inappropriately smile or smirk.

Watts said he and Shanann had had an "emotional" but civil conversation when he woke her around 5am, with talk of separating. She had said she was going to stay with a friend before he left.

But officers noticed Shanann's bag, wallet, medication, mobile phone, driver's licence and even her wedding ring were still in the house. They saw the sheets had been removed in the master bedroom, but Watts explained that was because Shanann had gone to bed straight from her flight.

When police questioned him about his relationship with his wife, he said it was "totally possible" she was having an affair, but he was not.

'SOMEONE ELSE'S BABY'

Nichol told police she had believed Watts was in the process of separating from his wife, and did not know she was pregnant. When Shanann disappeared, Nichol initially assumed she had walked out.

When she Facetimed Watts that evening, he was quiet, she said, and stared at her throughout the call. He was lying on a mattress with no sheets and told her he was cleaning the house for something to do, she said.

He said he had been sleeping, which she thought was bizarre when his family was missing. When she asked Watts about early newspaper reports his wife was pregnant, he said Shanann had only told him that on Monday morning after he woke her. She had said it was someone else's baby, he added.

Nichol said Watts asked repeatedly whether the situation would ruin their relationship, and seemed more worried about her than his family. She didn't believe he ever went to look for them.

As detectives closed in on Watts, friends and family began realising that this doting dad must have committed the most horrific crime.

Shanann's mother Sandra Rzucek was the first to offer the explanation to police, saying she had always believed he was a good husband, but had noticed he was "cold" towards his wife and children when he visited North Carolina.

She recalled one night when Shanann was vomiting because of her pregnancy and Watts had ignored her.

"She stated that Christopher is acting 'weird' and out of the ordinary," read the police report. "She said that Christopher is telling people, 'He has to go to work,' and that just doesn't seem right. She felt that he is going out to pour oil on the bodies to dispose of them somewhere."

'IT'S EMPTY HERE, I NEED MY FAMILY BACK'

Watts told one friend Shanann had said she was going to stay with friends. Others reported that he seemed "blank" and uncomprehending. "It's empty here, I need my family back," he said.

Finally, Nichol approached the police to tell them she didn't believe anything he said any more.

When she learnt his wife had been 15 weeks pregnant, she challenged him, saying he must have already known. She asked what he had done, but he said he would never hurt his family.

Nichol deleted all the information on her phone, telling police she was "grossed out by him".

The authorities later released her internet records, which showed she googled wedding dresses, sex tips, the phrase "Man I'm having affair with says he will leave his wife" and topics relating to "marrying your mistress".

They also found hours' worth of searches for "Shanann Watts" and, after the murders, a search for the phrase "can cops trace text messages" and "did people hate Amber Frey" — the mistress of a man who murdered his wife and unborn child. She also looked up how much money Frey made in her book deal and her net worth.

"He lied about everything," she told the Denver Post. "It got to a point that he was telling me so many lies that I eventually told him that I did not want to speak to him again until his family was found."

They never were. Within days, police spotted a fitted sheeted much like the one missing from the family home in a field south of the petroleum company's site.

On August 15, two days after the family's disappearance, Watts was arrested on suspicion of triple murder and first-degree unlawful termination of a pregnancy. The following day, he led police to where he had dumped the bodies.

He at first claimed his wife had strangled the girls, and he had strangled her to death in retaliation. But he pleaded guilty after he was offered a plea deal to avoid the death penalty.

Last week, Watts was handed three consecutive life sentences for the sickening killings of Shanann, Bella, Celeste and unborn baby Niko.

But the confusion and horror at what he did will linger in the memories of those who knew the family forever.

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