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"He is a monster."

Vanessa Curie is talking about her ex-boyfriend, Patrick Frazee — the man at the center of a homicide investigation that has gripped the country.

Frazee’s fiancée, 29-year-old Kelsey Berreth, disappeared from her home in Woodland Park, Colorado, on Thanksgiving Day. After a month-long investigation, Frazee, 32, was charged with two counts of murder and three counts of solicitation to commit murder. Prosecutors allege that he bludgeoned Berreth to death and burned her body. Berreth’s remains have not yet been found.

"He had no empathy for life," Curie said about Frazee, in an exclusive interview with NBC's "Dateline."

Patrick Frazee with ex-girlfriend, Vanessa Curie. Georgia Curie

Frazee’s attorneys declined to comment about Curie’s allegations as well as Berreth’s disappearance.

Frazee has not entered a plea in the Berreth case. He is scheduled to be arraigned on April 5.

Curie said she and Frazee started dating in 2010.

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"I was attracted to his sharp wit and he had a very explorative mind. He contemplated everything. And he was excellent at reading people," Curie told "Dateline" correspondent Andrea Canning.

But, four months into their relationship, Curie said Frazee started playing mind games on her.

“He began not calling me for days, and then calling me in the middle of the night telling me he had visions of me in a wedding dress. And we'd talk and argue for hours. And we'd end up winding right back into each other.”

The emotional abuse, as she described it, went on for a year. She said Frazee would put her on a pedestal, then tear her down. But, she said, she continued to be drawn to him.

As their relationship continued, Curie said she observed Frazee, a rancher and popular farrier, hit his dogs.

"Dateline" interviewed a man who knew another side of Frazee. Clint Cline said Frazee worked with his donkeys, and describes him as a “nice guy, very conscientious about his work, very concerned about the health and well-being of our animals, very great with his daughter.”

Kelsey Berreth was reported missing by her mother in Woodland Park, Colorado, on Dec. 2, 2018. Woodland Park Police Department

Curie and Frazee’s on-again, off-again relationship ended in 2014, when Curie said she came across the definition of a psychopath online.

“He fit the bill to a T. And that's when I left him.”

But Curie’s problems didn't end there. She said that just weeks after she broke up with Frazee, she went on a dating website and met a man who introduced her to methamphetamine. Her family said she became addicted, had several run-ins with the law and eventually landed in prison, serving a two-year sentence for drug possession, vandalism and escaping a community corrections facility.

Curie was at the Denver Correctional Facility for Women when she heard the news about Frazee being arrested for Berreth's murder — and about the other woman involved in the case, Krystal Jean Lee Kenney.

Kenney, a nurse from Idaho, had also been romantically involved with Frazee. Last month, she pleaded guilty to tampering with evidence. Kenney allegedly told investigators she helped Frazee clean up the bloody crime scene at Berreth's home and admitted to getting rid of her cellphone in an effort to disrupt the investigation, leaving many to wonder why she helped Frazee.

Curie believes she knows. She thinks Kenney was under his spell, just the way she had once been.

“He's a very, very complicated individual. And he's very, very smart. And, like I said, he can read people really well. And he knew how to press people's buttons.”

Though Frazee’s attorney declined a request for comment on his case, his examination of witnesses at a recent hearing suggests the defense will raise the issue of Kenney’s credibility — her previous lies to investigators and her friends and how she made statements about Frazee’s involvement in Berreth’s murder only after she knew of the potential charges against her and her plea deal was in place.

Cline does not believe his friend is capable of murder. Cline says there has been a rush to judgment. “We're supposed to be in a country where you're innocent until proven guilty,” he said.

“I'm not going to speculate. I'm going to wait and see what kind of evidence is presented," he said. "If the evidence comes out, OK, and I'm going to be shocked and amazed. But if it comes out the other way, there's a lot of people that are going to have to eat a lot of crow.”