FAIRFAX, Va. (AP) — A Brazilian au pair who fell in love with an IRS agent pleaded guilty to manslaughter on Tuesday in what prosecutors say was an elaborate double-murder scheme to frame another man in the stabbing of his wife.

For months after the killings on Feb. 24, 2023, it might have seemed as if Juliana Peres Magalhães and the IRS agent, Brendan Banfield, got away with murders, according to new details prosecutors revealed in court to support her guilty plea.

Christine Banfield, a pediatric intensive care nurse with a 4-year-old daughter, had been mortally wounded with stab wounds to her neck, and Brendan Banfield, her husband, and their live-in nanny both said they shot her apparent killer — a man who had been lured to the bedroom with promises of rough sex.

Magalhães had called 911 to the house in Herndon, Virginia, and was hyperventilating at the scene as she described the killings.

Detectives weren't buying it — but it took time to build their case. Meanwhile, the live-in au pair moved into the primary bedroom with Banfield and posted photos of them as a couple, authorities said. When she was arrested in October 2023, a picture of herself with Brendan Banfield was on the nightstand.

As she remained in jail for more than a year thereafter, she declined to say anything more.

A long-awaited forensics report on the blood spatter evidence then came in, and prosecutors said it showed that Brendan Banfield had smeared blood from Christine Banfield's wounds onto the body of Joe Ryan, the man they had tried to frame for stabbing her. Authorities arrested Brendan Banfield in September on charges of aggravated murder.

Banfield’s lawyer, John F. Carroll, said in court before he was denied bail in September that the evidence “just doesn’t add up” to him killing his wife.

In October, Magalhães agreed to cooperate with the police in her second interview since the day of the crime. Days later, on Tuesday, two weeks before she was scheduled to go to trial on charges of second-degree murder and felony firearm use, Magalhães pleaded guilty to Ryan’s killing, saying she had agreed to help the husband's ruse to kill the wife and make it look like they both shot a predator.

“Are you entering your guilty plea because you are in fact guilty of this offense?” Chief Judge Penney Azcarate asked Magalhães before accepting her plea to a single count of manslaughter, reduced from murder and a firearm offense.

“Yes,” she replied, softly.

The sentencing of Magalhães, who was raised in the outskirts of Sao Paulo, now awaits the conclusion of Brendan Banfield’s trial. Depending on her cooperation with authorities, attorneys said in court that they may agree for her to be sentenced to the time she's already served.

“Much of the information that led to this agreement cannot be made public at this time, due to the upcoming criminal trial against the other defendant in this matter," Fairfax County Commonwealth's Attorney Steve Descano said.

Viviane Magalhães, her stepmother, said she hoped her stepdaughter could soon return to Brazil and that “this nightmare ends.”

“We still can't figure this out — I believe she was fooled by this guy, he brainwashed her,” Viviane Magalhães said in Portuguese, referring to Banfield. “She was never a gold digger in Brazil, for many years she dated a man who was as humble as she was. We could never think of her living a situation like this.”

Laying out facts that Magalhães corroborated in court, prosecutors said that she made several 911 calls that day. The first lasted a few seconds, with no words — just the sound of someone’s guttural moaning in the background. Then, about 15 minutes later, another call went through, saying that an intruder had stabbed her friend. Brendan Banfield then took the phone, saying he had shot a man who was stabbing his wife.

An officer's body camera recording submitted in court last month shows Magalhães on her knees in the driveway, seemingly flummoxed and unable to catch her own breath.

“There was a lot of blood,” Magalhães said while hyperventilating. “Brendan said, ‘Please drop the knife, drop the knife,’ because he had a knife."

She later told detectives that she had shot the trespasser in the chest after Brendan Banfield shot him in the head.

In court Tuesday, prosecutors alleged that she had been lying as part of a ruse to lure someone else into the home to be framed in the wife's murder.

Affidavits have said Magalhães began working for the Banfields in late 2021. Deputy Commonwealth’s Attorney Eric Clingan said in court that the au pair and the husband began having an affair in August 2022. Shortly thereafter, Brendan Banfield began plotting to kill his wife, Clingan said.

To cover the ruse, Clingan alleged that Brendan Banfield created a profile for his wife on a social networking platform for people interested in sexual fetishes and matched her with Ryan. Soon, they were chatting through Telegram, an encrypted messaging application, with Magalhães pretending to be Christine Banfield on a voice call. Ryan agreed to come to the house for what appeared to be a consensual sexual encounter.

“At various points before the 24th, Peres Magalhães expressed to Brendan Banfield that she did not believe he would go through with this plan and, at other times she told him she did not want to continue,” Clingan said. “But he insisted that it was too late for her to back out.”

Clingan said Magalhães and Brendan Banfield left the daughter in the basement and then followed Ryan to the bedroom, guns in their hands.

Authorities monitored her phone conversations at the Fairfax County jail. In one call last month, Clingan said Brendan Banfield's mother, who has paid for the au pair's legal defense, discussed the consequences that “snitches” in the jail would face.

In another, between Brendan Banfield and the au pair, Magalhães said: “I hope you are not just staying with me because you are afraid I’m going to turn against you.”

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Associated Press writer Mauricio Savarese reported from Sao Paulo, Brazil.

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Olivia Diaz is a corps member for The Associated Press/Report for America Statehouse News Initiative.