The book was called Hold Me Tight.

Shanann Watts, 34, ordered a copy for her husband, Chris, 33, during the final days of their marriage - a couple's guide to forging deeper bonds, and a last act of desperation to save their fractured relationship.

For weeks, Shanann had been sending Watts anguished messages, pleading with him to hold her, to desire her, to come back to her. He put the book in a trash can in the garage without ever opening it.

When police found it there, still sealed in its Amazon delivery box, Shanann had been dead for three days - her life taken by the same hands she had been begging to feel. 

She was not alone. The couple's daughters, Bella, four, and Celeste, three, were also dead. Their unborn son, Nico, was never given the chance to draw breath.

Watts murdered Shanann and the girls in the early hours of August 13, 2018, then disposed of their bodies at a remote oil field north of Roggen, Colorado.

He later launched a public appeal, claiming Shanann had vanished with their daughters after an 'emotional conversation' early that morning. Despite playing the concerned husband for the cameras, he knew exactly where they were all along.

Watts was arrested two days later and eventually admitted to killing Shanann and smothering their children. He is now serving life.

His affair with co-worker Nichol Kessinger would become one of the most notorious elements of the case. But buried deep within investigative files reviewed by the Daily Mail is the account of another woman who said she shared a frightening sexual encounter with Watts after meeting him on Tinder months earlier.

The documents also reveal overlooked details of Shanann's desperate attempts to save their marriage - including the unopened relationship guide and additional evidence suggesting Watts's infidelity may have begun far earlier than previously understood. 

In the weeks before her death, Shanann was struggling to understand why the husband she had known for eight years had suddenly grown so cold.

She had travelled to North Carolina with Bella and Celeste on June 27 for a six-week visit with family. Watts stayed in Colorado for the first five weeks, citing work commitments, before joining them for the final seven days.

While Shanann was away, he was pursuing a secret relationship with Kessinger.

Even before Watts arrived in North Carolina on July 31, Shanann sensed something had changed.

'How many times do I have to ask you to hold me? You hate me that much?' she wrote.

'I don't hate you,' Watts replied. 'I will fix this. It will be better.'

But the strain extended beyond his refusal to show affection.

Shanann was pregnant with their third child, and, according to messages she sent friends, Watts had told her he did not want another baby and raised the possibility of an abortion.

She searched for couples counselors, asked friends to pray for them and planned a romantic weekend in Aspen, hoping to reconnect.

But investigative files compiled by police suggest Kessinger may not have been the first woman Watts pursued behind Shanann's back.

The woman, Amanda McMahon, told detectives she had met Watts on Tinder in February or March 2018 - around six months before the murders.

They arranged to meet in a Chick-fil-A car park, where he arrived in a dark-colored pickup and claimed he was separated from his 'babies' momma,' who would not allow him to see his children. They then drove separately to McMahon's home for sex.

The encounter quickly became unsettling, she said.

McMahon told detectives Watts pulled her hair and wrapped his arms around her neck. She described the encounter as a 'rape fantasy' and said she had to push him away at one point.

Though she recalled feeling humiliated by the 'fast and furious' encounter, she said she did not fear for her safety.

'No radars went off or anything,' she told investigators.

McMahon - who works as a barber in Greenley, Colorado - said she was 99 percent certain the man was Watts and accurately described his tattoos and workplace. But she acknowledged she could not identify him with enough confidence to testify in court.

Watts later denied ever meeting McMahon, insisting his only extramarital affair was with Kessinger. 

But six days after the murders, police received another tip suggesting there may have been yet another woman.

At approximately 11am on August 19, four emails arrived from the anonymous address familyheating@aol.com.

The sender warned that they were 'partly blind' and that their typing was poor. The first message was riddled with errors, but its allegation was clear.

The writer named a woman called Heidi Ferris and claimed she had spoken of an on-and-off affair with 'a guy named Chris' who was married with two children.

The pair allegedly communicated through a hidden application disguised as a calculator. Entering a secret code, the sender claimed, transformed it into a private communication platform.

'She may by now have erased any messages,' the tipster wrote, 'but if you have his phone I'd check for that app.'

Other emails contained contact details for Ferris's husband, who the sender said worked for AZCO, a contractor linked to the oil and gas industry.

The discovery documents do not identify the sender, establish that Watts knew or confirm that an affair took place.

But one element of the tip was correct.

Watts did have a calculator-style application concealing intimate material on his phone.

That discovery unlocked a trove of photographs and videos charting his relationship with Kessinger.

Kessinger, then 30, was a quality-control contractor at Anadarko, where Watts worked. While Shanann and the girls were in North Carolina, the pair visited museums, attended a drag-racing event and took an overnight camping trip to the Great Sand Dunes and Zapata Falls.

They exchanged explicit photographs and spoke for hours, sometimes while Shanann was calling and messaging Watts.

On July 18, Watts transferred a batch of semi-nude images into the hidden calculator app. In some, investigators noted, his reflection was visible in a mirror behind Kessinger.

Eight days later, he moved another nude photograph into the app while speaking to Shanann on the phone.

The images were only one part of the digital trail.

Kessinger's internet searches offered a more revealing glimpse into how seriously she viewed the relationship.

On July 24, Kessinger searched Google for: 'Man I'm having affair with says he will leave his wife.'

Shortly after midnight on August 4, she spent roughly two hours browsing wedding dresses.

Four days later - as Shanann told friends that Watts had rejected counseling, refused to hug her and said they were no longer compatible - Kessinger searched for information about 'marrying your mistress.'

Her browser history also documented preparations for their sexual encounters.

On August 11, hours before she was due to see Watts, Kessinger spent approximately 45 minutes searching for advice on preparing for anal sex. The searches progressed to Pornhub videos involving interracial sex and threesomes.

The investigator who compiled the phone review noted that this was 'by no means the only time' Kessinger had searched for pornography.

One search entry stood apart from the rest. 

On September 1, 2017 - nearly a year before the murders and months before Kessinger said her relationship with Watts began - she searched the internet for 'Shanann Watts.'

The investigative files do not explain why, nor has Kessinger ever addressed the search publicly.

She searched Shanann's name again on August 14, the morning after she disappeared with her daughters.

Later that afternoon, she searched: 'Can cops trace text messages,' followed by 'How long do phone companies keep text messages' and 'Difference between text message content and text message detail.'

Investigators noted that the searches had been deleted. Kessinger also continued Googling Shanann's name and erasing those entries.

By then, Watts's story was unraveling.

He told investigators Shanann had returned from a business trip in the early hours of August 13 and that they held an 'emotional conversation' about separating before he left for work.

According to Watts, Shanann remained in bed and said she planned to take the girls to an unnamed friend's house. He did not ask which friend.

Her final message had been sent at 12.25am, shortly after her flight landed.

'Landed,' she wrote, followed by three sleeping-face emojis. 

Within hours, she was dead.

Virtually no one close to Shanann believed Watts' version of events.

Her car was still in the garage with the girls' car seats inside. Her purse, wallet, medication and phone were in the house. She had also missed a prenatal appointment - unthinkable, friends said, for a woman so organized.

Nickole Atkinson first raised the alarm. Shanann's mother told police she believed Watts was involved and urged them to check the GPS on his work truck.

Cassie Rosenberg similarly told investigators that if they established where the truck had gone that morning, they would find Shanann and the children.

Watts, meanwhile, was working hard to make it appear as though he had been abandoned.

After disposing of his family's remains, he texted Shanann's phone: 'If you take the kids somewhere, please let me know where they are at!'

His phone activity suggested he was already behaving as though life would continue on as normal without them.

He called the girls' school, said Bella and Celeste would no longer attend because the family was moving, then asked: 'They're not there, are they?'

At 9.29am, he transferred one final semi-nude photograph of Kessinger into the calculator app.

At 10.10am - during what the investigator described as a 'respite' after the murders - Watts searched for the lyrics to Metallica's Battery.

The song includes references to violence and the repeated line: 'Cannot kill the family.'

Later that morning, as Shanann's friends grew increasingly alarmed, Watts searched for hotels in Aspen and browsed Groupon - the destination she had chosen for the weekend away she hoped might save their marriage.

That evening, neighbor David Colon later recalled finding Watts cleaning the house from top to bottom.

By the following day, with his pregnant wife and daughters officially missing, Watts confirmed his participation in a fantasy football league.

As more details emerged, Kessinger began distancing herself.

She deleted Watts's contact information, photographs and messages, later telling investigators she had done so after learning Shanann was pregnant and realizing he had lied about the status of his marriage.

Kessinger spoke to investigators on August 16 and handed over items Watts had left at her home.

'I legitimately think his cheese was sliding off his cracker long before he met me,' she told them.

Within hours, Watts failed a polygraph and began to confess.

At first, he blamed Shanann, claiming he saw her strangling Celeste on a baby monitor after killing Bella, and that he then strangled his wife in a rage.

Investigators did not believe him.

Watts eventually admitted killing Shanann, Bella and Celeste. In November 2018, he pleaded guilty to three counts of first-degree murder, four additional murder counts, unlawfully terminating Shanann's pregnancy and three counts of tampering with a deceased body.

He is serving five life sentences, three of them consecutive.

Kessinger was never accused of any wrongdoing, but her search history after Watss's arrest provided one final interesting glimpse into her thinking.

She looked up Amber Frey, the former mistress of convicted wife-killer Scott Peterson, searching for information about her book deal, net worth and whether or not the American public hated her.

Finding herself at the center of another high-profile family-murder case, Kessinger appeared to be studying what had happened to Frey to know what her own future might hold.

She gave only one interview to the media and has since vanished from the public eye.

'I don't think there is a logical explanation for what he did,' she told The Denver Post in 2018.

'It's a senseless act, and it's horrific.'