Killer Chris Watts' Letters From Prison Detailing His Murders Are Heartbreaking

Callous, cold-blooded killer Chris Watts is said to be in an "a dark place" following the release of a new Netflix documentary that details how he strangled his pregnant wife, Shanann Watts, and smothered their two daughters, Bella and Celeste.

American Murder: The Family Next Door is currently the most-watched program on Netflix, and details his horrific, sickening crimes.

Watts, who is serving three life sentences for the grisly murders, will never get to see the doc — and that distresses the killer.

"Just knowing that the documentary is out there has sent Chris to some dark places," a source told PEOPLE on Monday, October 5.

"He hates knowing that it's out there but realizing that he will never see it. He wants to know what the documentary looks like and how it tells the story."

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Not even being behind bars can quell Watts' evident narcissism.

But there's not a pity party in sight for the man, who planned and executed the death of his family so he could run off and be with Nichol Kessinger, the colleague he had begun secretly dating only a few weeks before.

In excerpts of letters published in the 2019 book Letters From Christopher: The Tragic Confessions of the Watts Family Murders by Cheryln Cadle, who struck up a correspondence with Chris shortly after he was sentenced to life in prison in November 2018, he said he planned the murders for hours prior to executing them.

"I walked away and said, 'That's the last time I'm going to be tucking my babies,'" he wrote in a letter, according to the Daily Mail. "I knew what was going to happen the day before and I did nothing to stop it. I was numb to the entire world."

"All the weeks of me thinking about killing her, and now I was faced with it," he wrote about his wife. "I knew if I took my hands off of her, she would still keep me from Nikki."

INSIDE SHANANN WATTS' LOVE LETTERS TO HER HUSBAND CHRIS BEFORE SHE WAS MURDERED

The letters also reveal that Chris first attempted to smother his daughters in their beds before returning to his own bedroom, where he argued with Shanann and killed her soon thereafter. The girls, however, then "woke back up," he wrote. "It makes the act that much worse knowing I went to their rooms first and knowing I still took their lives at the location," he continued, presumably referring to the facility where he hid the three bodies.

There has been renewed interest in Watts since the documentary began streaming on Netflix on September 30, which has resulted in the 35-year-old getting fan mail.

The jailbird is corresponding with a number of female fans who are all too willing to stay in touch with him.

"He got a lot of letters at first," a source told PEOPLE. "Many of them are from women who thought he was handsome and felt compassion for him. He had nothing better to do, so he wrote them back. And he started having pen pals. A couple of them stood out, and they've kept in contact."

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"They have compassion on him, despite what he did," the insider shared.

Watts is currently locked up at the maximum-security prison Dodge Correctional Institution in Waupun, Wis. He is on lockdown for 23 hours a day and is not eligible for parole.

Not only are people curious about the case in general, but employees in the prison are intrigued by Watts. "There’s a lot of curiosity about him in prison," the insider said. "He’s the most high-profile inmate and what he did is incomprehensible, so everyone wants to know more about the case."