A bucolic Virginia neighborhood. A seemingly normal family of three. A Brazilian au pair. A double murder.

These are all parts of a complex puzzle investigators are still working to determine who killed Christine Banfield — a wife, mother and Fairfax County NICU employee — and Joseph Ryan, the 38-year-old man who showed up at her home armed with a knife, in Herndon, Virginia, in February 2023.

Part of that puzzle is in the process of being solved as Juliana Peres Magalhaes, Banfield's 23-year-old au pair and a Brazilian national, prepares to stand trial for second-degree murder and use of a deadly weapon during the commission of a crime in Ryan's shooting death.

Authorities have not filed any charges in connection with Banfield's death.

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Juliana Peres Magalhaes mugshot

Juliana Peres Magalhaes was charged nearly eight months after she fatally shot Joseph Ryan – the man had just stabbed her affair partner's wife to death. (Fairfax County Police)

The initial crime

The mystery began on Feb. 24, 2023, when Magalhaes told police she left Christine and husband Brendan Banfield's home in the 13200 block of Stable Brook Way in Herndon to take their young daughter to the National Zoo. She told authorities that she had begun driving but realized she forgot the lunches she packed for their excursion back inside the house, so she turned around and noticed an unfamiliar car in the driveway.

She then reportedly called Brendan, a former criminal investigative agent for the IRS who had at that point left for work, and told him about the unknown car in their driveway. The pair decided to meet at the Banfields' home and walk inside together, as the Washington Post reported.

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Juliana Peres Magalhaes

Magalhaes is charged with second-degree murder and use of a deadly weapon during the commission of a crime. (Instagram)

Initially, Magalhaes told police that when she and Brendan walked inside, they saw an unknown man, Ryan, holding Christine at knifepoint. She allegedly described him as an intruder. Ryan was apparently fully clothed while Christine was naked in the main bedroom of the house.

It remains unclear exactly what transpired inside the home that Friday morning, but Magalhaes and Brendan apparently both admitted to shooting Ryan while the man was holding a knife to Christine. Ryan died inside the home while Christine suffered stab wounds to the neck and ultimately died in the hospital.

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Christine Banfield

Christine Banfield was stabbed to death in the bedroom of her Fairfax County, Virginia, home. (Facebook)

Fairfax County police began investigating, telling reporters during a news conference later on the day of the murders that someone inside the home called 911 that morning. Court documents would later reveal that Magalhaes and Brendan both called 911 multiple times that morning. 

"This is evolving and changing. This is very dynamic."

— Fairfax County Police Department Chief Kevin Davis

Fairfax County Police Department Chief Kevin Davis said during the press conference that there were no additional suspects in the case other than the four adults who were inside the home at the time of the double homicide. He also said there were no signs of forced entry and that "everyone inside the home" was "known to each other."

13200 block of Stable Brook Way in Herndon

Fairfax County police responded to the double homicide in the 13200 block of Stable Brook Way in Herndon, Va., on Feb. 24, 2023. (FOX 5 DC)

The Banfields' daughter was home at the time of the murder, the police chief said at the time.

Investigation revelations

As Fairfax authorities continued to investigate, they began to unravel a complex web of details about the four adults tied to the double murder.

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Prosecutors now allege in court documents that Magalhaes and Brendan had been having an affair, unknown to Christine. The pair allegedly went to a shooting range just weeks before the double murder, according to the Post.

Prosecutors also allege that a computer at the Banfield home was tied to an account on a sexual fetish website, the Post reported.

Fairfax Co. Police Chief Davis

"This is evolving and changing. This is very dynamic," Fairfax County Police Department Chief Kevin Davis said at the time, adding that there were no additional suspects in the case other than the four adults who were inside the home at the time of the double homicide. (Facebook)

While the account on that computer appeared to show a photo of Christine in a bathing suit, it is unclear exactly who was communicating on the account. The profile also apparently did not display "one iota of evidence that she was into knife play, binding, BDSM," prosecutor Eric Clingan said in court, according to the Post.

Ryan, the man who held Christine at knifepoint, also apparently had an account on the website and had been communicating with whoever was accessing the site from the Banfield computer.

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Authorities eventually arrested Magalhaes in October 2023 after she moved in to the Banfields' main bedroom and placed a framed photo of herself with Brendan on a nightstand beside the bed. A grand jury indicted the 23-year-old in April, and her trial is scheduled to take place in November.

Framed photo of Brendan Banfield and Juliana Magalhaes

A framed photo of Brendan Banfield and Juliana Magalhaes and the mistress's lingerie were found in the room where the double homicide occurred, according to prosecutors. (Fairfax County Commonwealth Attorney's Office)

Her attorney, Ryan Campbell, said Brendan fired at Ryan first while the man was holding a knife to his wife's neck and then asked his client to retrieve another gun from the closet of the main bedroom. Then Magalhaes fired at Ryan because she believed he posed a threat to her employers, according to the Post.

"You have a stranger in the house and a dying woman."

— Attorney Ryan Campbell

"Mr. Banfield, who is of law enforcement, then shoots him once," Campbell said in court, the Post reported. The attorney did not respond to an inquiry from Fox News Digital.

The Banfield home in February 2023

Authorities eventually arrested Magalhaes in October 2023. (FOX 5 DC)

Magalhaes' mother maintains that her daughter is not guilty.

"I pray for the prosecutors and the judge to understand who is guilty in this case, because it is not Juliana," Marina Peres Souza told the Washington Post in Portuguese.

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In a June email to her mother shared with the Post, Magalhaes wrote, "I am tired of this place, this situation. I am unhappy, and nothing makes me happy. I just want to get out of here and go back home to be with you guys."

Brendan is no longer employed by the IRS, the agency confirmed to Fox News Digital on Thursday. He invoked his right to the Fifth Amendment in response to questions about his alleged ties to the case during a preliminary hearing in April.