Chris Watts’ Mistress Revealed Affair to Police After His Wife & Kids Vanished: 'Wanted to Help'

The mistress of admitted triple-murderer Chris Watts said she told police about the affair after he behaved suspiciously when his wife and two daughters went missing and his lies to her were exposed.

Nichol Kessinger, 30, spoke out for the first time in an interview with The Denver Post published Thursday. Kessinger, who met Watts through work, was the woman whose name was redacted from an affidavit for Watts’ arrest which said he was having an affair, a law enforcement source confirms to PEOPLE.

Watts, 33, pleaded guilty last week to the August murders of his wife of nearly six years, 34-year-old Shanann Watts, and their daughters, Bella, 4, and Celeste, 3. He will be formally sentenced to life in prison on Monday.

RELATED: Behind Chris Watts’ Decision to Plead Guilty — ‘Eventually He Acknowledged His Life Was Over’

Kessinger told the Post that on Aug. 13, the day Shanann and the girls went missing, Watts texted her saying he’d been busy but the two conversed normally throughout the workday.

Chris Watts
Chris Watts

At 3:45 p.m., however, she said Watts texted her that his family was “gone,” and later explained that Shanann had taken the kids to a playdate and hadn’t returned. While Kessinger was worried about Watts’ wife and two daughters, she noted Watts seemed unperturbed and didn’t show emotion.

RELATED: Chris Watts’ Mistress Breaks Silence About Affair with Triple-Murderer: ‘He Lied About Everything’

Later, Kessinger saw news reports that Shanann and the girls were missing — and that Shanann had been 15 weeks pregnant. This shocked Kessinger because Watts had told her since their affair began in early July that he was in the process of getting divorced, and then later told her their divorce was final.

“I thought, ‘If he was able to lie to me and hide something that big, what else was he lying about?’ ” she told the paper.

Shanann Watts and her daughters
Shanann Watts and her daughters

Kessinger subsequently became suspicious of Watts and frightened for Shanann and the girls. She peppered him with questions about the case but Watts showed no emotion, she told the paper.

“It seemed off,” she said, and added that she later cut off contact with him.

RELATED: Why Did Chris Watts Murder His Wife & Kids? D.A. Has ‘Partial Motive’

“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 said.

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On the morning of Aug. 15, Kessinger called the Weld County Sheriff’s Office and discussed her affair with Watts and his lies to her, she said. She also spoke with investigators from the FBI. Later that night, Watts was arrested.

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

RELATED: As Chris Watts’ Parents Defend Him, Murdered Wife’s Family Slams ‘Grotesque and Utterly False Statements’

After his arrest, under police questioning, Watts allegedly said he would “tell the truth” after investigators told him they found out he was having an affair with a co-worker, according to the arrest affidavit.

He then admitted he killed Shanann after flying “into a rage” when, he claimed, he saw her strangling one of their daughters via a baby monitor after he had told her he wanted a separation, according to the arrest affidavit.

But in court earlier this month, Watts pleaded guilty to nine charges, according to prosecutors: five counts of first-degree murder, one count of unlawful termination of pregnancy and three counts of tampering with a dead body.

In pleading guilty, Watts essentially admitted his earlier explanation was a lie.