Chris Watts’ secret lover was searching Google for wedding dresses and topics relating to “marrying your mistress” just days before he murdered his wife and family.

Nichol Kessinger, who worked with Watts, also Googled how much money author Amber Frey made in her book deal and her net worth.

Frey was the mistress of a man who murdered his wife and unborn child. She wrote a book about it in 2004 and it’s still on shelves now, selling for $12 on Amazon.

Ms Kessinger also searched “did people hate Amber Frey”.

New documents — released by the Weld County, Colorado, District Attorney’s Office — reveal Ms Kessinger’s internet activity. It shows that on July 24 she searched Google for the phrase, “Man I’m having affair with says he will leave his wife,” People reported.

Watts strangled his wife Shanann, who was pregnant with their son, and smothered their two daughters, Bella, 4, and Celeste, 3, in Colorado, US, on either August 12 or 13. A week earlier, the documents show that Ms Kessinger — who seemed certain Watts was going to end his marriage — spent more than two hours searching the internet for wedding dresses.

Ms Kessinger spoke about the case for the first time in an interview with The Denver Post on November 15 where she claimed the triple-murderer was a liar.

She said she was tricked into believing Watts was a loving father, finalising a divorce and she had no idea his wife was 15-weeks pregnant.

“He lied about everything,” Ms Kessinger, 30, told The Denver Post.

The documents stated that on the night before the murders, Ms Kessinger also spent 45 minutes Googling “how to prepare for anal sex,” and “the anal sex guide”.

This was soon after she began looking at videos of threesomes on a pornographic website.

Meanwhile, a search of Watts’ phone found hidden pictures of a nude or semi-naked Ms Kessinger. They were located in a secret calculator app that was only accessed by typing in a four digit code.

The affair unfolded as Shanann and the girls spent several weeks away from Watts over the summer visiting Shanann’s family in North Carolina — a period during which Shanann continuously reached out to him in hopes of repairing their struggling marriage, the documents revealed.

In a text sent to her friend Ady, Shanann wrote out the entire speech she planned to deliver on Monday, after she had returned home and got some rest.

“Can you please tell me something, because just like you, I’m in my head? I try to fix things and make them better and this is making me crazy. I know that you need time. I want to give you what you’re asking for and respect your space, I need some time. This place that I’m in, in my head, is not a good place,” read the text.

“lt is not healthy for me, or Niko. I need you to help me help you. I need you to give just a little bit of what I did, or didn’t do, so I’m not going crazy in my head to figure it out. I know I can’t fix this by myself; that, we are going to have to work together.”

Niko was the name of their unborn child.

After they returned home to Frederick, Colorado, Shanann took a short solo work trip. She returned home again on August 13, when prosecutors say Watts strangled her and smothered the two girls with his bare hands.

Watts initially issued a public appeal for his family’s safe return and even contacted his daughters’ school saying they would not be attending.

It was during this time when Ms Kessinger claimed to have realised he was still married and his wife was pregnant.

According to the Denver Post, after Shanann and the girls disappeared, Watts texted Ms Kessinger to say that he had been busy and the two chatted like normal throughout the workday.

It wasn’t until 3.45pm that same day, when Watts texted Ms Kessinger saying that his family was “gone”, explaining Shanann had taken the girls to a play date and had not returned.

He seemed casual and didn’t show any emotion, she told the publication.

When news reporters showed up at the Watts’ family home, Ms Kessinger said she was “very confused why the media was at his house”.

“When I read the news, I found out he was still married and his wife was 15 weeks pregnant,” Ms Kessinger said.

The Denver Post reported that while at work on August 14, Ms Kessinger texted Watts, who she had been dating since July, pushing him to tell what he knew about their disappearance and asking what he had done. He told her he would never hurt his family, she said.

“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,” she told the publication.

Taking matters into her own hands, the next morning Ms Kessinger reportedly called the Weld County Sheriff’s Office to tell them about her relationship with Watts and his lies, she said. Ms Kessinger met with FBI investigators that day.

“I just wanted to help,” she said. “With a pregnant woman and two children missing, I was going to do anything that I could.”

But, according to People, authorities also revealed that she acknowledged deleting all of Watts’ information from her phone prior to meeting with police.

The documents further reveal that authorities who examined Ms Kessinger’s phone found hours’ worth of searches for “Shannan Watts” and, after the murders, a search using the phrase “can cops trace text messages”.

She said she was shocked by Watts’ arrest. But she has never doubted that he killed his wife and kids.

“I don’t think there is a logical explanation for what he did,” she told The Denver Post. “It’s a senseless act, and it’s horrific.”

Watts was arrested on August 15; the next day the bodies were found on the oilfield property of his former employer.

When Ms Kessinger revealed her identity to the media, she said she “barely knew” Watts and that “we had just met.” She said the two were taking it slow and didn’t discuss any long-term plans.

On August 20, Watts was charged with nine counts including murder in the first degree, unlawful termination of pregnancy and tampering with a deceased body.

Originally, Watts faced the possibility of the death penalty or life in prison without parole.

But with the agreement of Shannan’s family, the death penalty was eliminated from consideration in exchange for pleading guilty.

At his sentencing, Shannan’s father, Frank Rzucek, called him a “heartless monster.”