Christopher Watts was charged Aug. 20 with multiple counts of first-degree murder, unlawful termination of pregnancy and tampering with a deceased human body.

He pleaded guilty, admitting that he murdered his pregnant wife and young daughters, loaded the bodies into his truck and dumped them at an oil work site.

Just days after his admission, a letter arrived.

“I found myself thinking a lot about you,” Tatiana, a Brooklyn-based woman, confessed to the now-convicted killer, “I figured life is too short to hold back … so here I am!”

The 29-year-old enclosed a bikini-clad photo of herself on a beach. “So you can place a face to the words. I know what you look like so I thought I’d make it fair,” she flirted. “I hope I’ve put a smile on your face.”

Tatiana wasn’t the only one.

Watts has been incarcerated since his August arrest. In November, a Colorado judge sentenced him to three consecutive life terms in prison — one for each murder victim. In his time behind bars, documents obtained from the prosecutor’s office by The Washington Post show, Watts received scores of letters from hopeful suitors.

‘I just became attracted to you’

Candace, a 39-year-old mother of two, wrote multiple times; her second letter ended with #TEAMCHRIS #LOVEHIM and a doodled heart. “I’ve been watching your interview and I just became attracted to you (don’t ask me why),” she said in one missive, adding that if he wrote back she would “be the happiest girl alive.”

Another woman named Christan began by “addressing the elephant in the room. No, I’m not a creeper or crazy.” She was drawn to Watts when she watched him take a deep breath as the judge read out his murder charges.

She said, “I know how alienating this process can be.”

Tammy, 36, described herself as “a simple girl living in a small town” and included photos. She noted that it was her first time writing to an inmate and that she was “actually very nervous.”

The Ohio-based woman asked Watts, “Why is someone as pretty as me single? And writing to someone in jail?” (She recently came out of a bad breakup, she explained.)

What explains the allure?

How a woman could fall for a man jailed for killing his family might seem perplexing, but this decades-old phenomenon is far from unusual. Front-page offenders — like Jeffrey Dahmer, Ted Bundy, Charles Manson and the Menendez brothers — have also been pursued behind bars by countless women.

The incarcerated individual is likely to have become part of a sadomasochistic fantasy for many of these women, given how popular true-crime shows are and how accessible the offenders are, Katherine Pier, a psychiatrist on the faculty at the University of California at San Francisco, told The Washington Post.

“It’s a way of flirting with danger while risking nothing,” said Pier, who has worked with felons. “The women writing killers are often victims of abuse and gravitate toward aggressors. Getting involved with a man behind bars puts them in positions of control. These women will most likely never have the chance to meet the man they’re pursuing. And if they did, they’d be protected by the prison system.”

Sheila Isenberg, author of “Women Who Love Men Who Kill,” echoed Pier.

It was less about chasing celebrity or being with a notorious killer, Isenberg said. Being in love with a man behind bars is exciting. “You don’t know what’s going to happen. There’s always an adrenaline rush."

Fame, social media play a part

Then came a second type of woman who vies for the attention of someone like Christopher Watts.

Isenberg attributed the shift to the current celebrity-worshiping culture and the rise of social media platforms, which have “allowed for an explosion of female fans to come out of the woodwork.”

In part, she said, the women who write to killers like Watts want to be famous and well-known also. It is more a case of “Hey I want to be famous; pick me.”

In the past, true-crime narratives making national headlines were reserved mostly for mass murderers. Now, serial-killer groupies have open communication forums. They generate Facebook groups and Reddit posts, giving notice to men who otherwise would have been little-known, garden-variety killers.

The more famous the person, the more magnetic he is.

“It makes domestic murderers like Watts public figures. They become notorious,” said Isenberg, who is working on a follow-up book, “More Women Who Love Men Who Kill.”

“The media frenzy and online attention around people like Watts prompted me to realize there is a whole new genre of relationships between murderers and women on the outside.”

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Female inmates were forced to expose their genitals in a ‘training exercise.’ According to a court ruling, that was legal.

The women were ordered to strip. Those on their periods were asked to remove their tampons and pads.