FAIRFAX COUNTY, Va. (7News) — Warning: this story will contain details some readers might find disturbing. Viewer discretion is advised.

The Brendan Banfield double murder trial on Tuesday began with opening statements, before the au pair involved in the alleged scheme testified for almost two hours to close out the day.

WATCH BELOW OR HERE:

Banfield is accused of killing his wife and another man at his Fairfax County home in February 2023.

According to prosecutors, Banfield and Juliana Peres Magalhaes - the family's Brazilian au pair, with whom he was having an affair - carried out an elaborate plot that involved them creating a fake profile of his wife on a fetish website to lure a man, in an attempt to stage a home invasion gone wrong. Detectives said Banfield shot the man, Joseph Ryan, and stabbed his wife, Christine Banfield.

PREVIOUS | Jury selected in the Brendan Banfield double murder trial after several hours

"The key evidence in this case is going to be the cooperating witness, Juliana, the Brazilian au pair, as well as the digital evidence connecting the two their extramarital affair, and then the setup in this case to make the murder of Christine and Joseph Ryan seem like it was self-defense,” said former federal prosecutor Neama Rahmani.

The prosecution and defense each spent about 15 minutes on opening statements, before the prosecution began calling their list of witnesses.

Both sides finished questioning the first five witnesses before getting to the last witness of the day: Magalhaes.

For almost two hours, prosecutors asked the au pair several questions about her relationship with both Brendan and Christine Banfield, the alleged plan, and the day of the alleged double murder before the judge ended the day. The prosecution did not finish their line of questioning, meaning Banfield's lawyers have not yet had a chance to ask their questions.

Prosecutors began their questioning by getting Magalhaes to describe the evolution of her relationship with Mr. Banfield.

She said she arrived in the country in October 2021, and she maintained a strictly professional relationship with the family while caring for their child. She said she felt welcomed, and she spoke more with Christine Banfield and the child than she did with Brendan.

Magalhaes said her sexual relationship with Mr. Banfield began in August 2022, and she had told some of her friends.

At this point, the prosecution showed the jury some pictures and a video Magalhaes posted on social media. In each of these posts - which include one picture where the two are in a tub of some sort, another picture showing a hand on her leg, and a third picture of the two in what appeared to be a restaurant - she covered Banfield's face.

In October 2022, Magalhaes said Banfield began talking about wanting to marry her and have kids. It was around this time when he allegedly mentioned a plan to "get rid" of his wife, telling the then-au pair divorce was not an option because of money and he did not want to share custody of their child. Magalhaes said on the stand she thought he was joking.

That same month, the two went to a shooting range one time, where Mr. Banfield allegedly taught her to shoot. The prosecution showed the jury pictures of the document she signed at the range and a social media post showing her shooting there.

While on the stand, Magalhaes said they went to the shooting range again in December, and it was after this, in January 2023, that she and Mr. Banfield created an email address with Christine's name for their fake account on the fetish website, FetLife, using Christine's laptop. She said this was all Brendan's idea.

The prosecution asked how the two were able to get access to that laptop, to which Magalhaes responded it was in Mrs. Banfield's backpack that she left by the door when she came home from work.

Magalhaes then told the prosecutor they used Mrs. Banfield's picture for an account with the username "Annastasia9," using Christine Banfield's picture.

In using this account, Magalhaes explained, the two would look for men who had aggressive sexual preferences on Christine Banfield's laptop while she was asleep or in another room of the house - which is also how they accessed her cell phone - with Brendan typing out the messages. If Magalhaes sent messages, she said she did it with direction from Mr. Banfield.

The au pair said they only used this laptop when she was home from work, to make it look like it was Christine sending these messages. She told the prosecutor this was Brendan Banfield's idea because he anticipated a criminal investigation into the deaths that resulted from this alleged plot. According to Magalhaes, Mr. Banfield told her there would be an investigation because there would be a murder, the police would know where Christine's cell phone and laptop would ping when messages were sent.

The prosecution then rattled off a list of questions about interactions on the FetLife account with other users Banfield and Magalhaes never met. Magalhaes said they stopped communications with users who requested to meet in public, at a hotel, or at their home. Their plan, she claimed, was to get a user to meet at the Banfield home.

Eventually, they chatted on the site with Joseph Ryan, who went by the username TacoSupreme7000.

According to Magalhaes, Ryan agreed to come to the house and play out a sexual fantasy involving knives and ropes, which made Brendan Banfield comfortable luring him as part of the alleged plan.

At this point, Magalhaes said, they began communicating with Ryan by text and voice call using the Telegram app. She said Brendan created the account on Christine's laptop, and they used that account when they were in possession of her laptop and phone.

The first time Magalhaes spoke with Ryan over the phone, she claimed he was surprised with her Brazilian accent.

The prosecution showed the jury some of the messages exchanged between Ryan and the fake Telegram account, including Ryan's message saying he was looking forward to their meeting on the day of the eventual alleged double murder, a picture sent by Ryan showing a knife and ropes, and a message from Brendan Banfield and Magalhaes saying the family dog will be in the basement and for Ryan to leave it alone when he arrived to the home.

With the alleged staged home invasion now set up, Magalhaes said Brendan Banfield told her to get a new cell phone with a new Apple ID two days before the meet-up, because she had pictures of them together on her old phone. She said he also changed his phone.

Around this time, the au pair said Mr. Banfield changed the windows so they would be sound-proof, and tested it out by seeing if she could hear him screaming in the bedroom from outside. She also said he checked to see which neighbors had cameras.

Magalhaes normally parked her car in the driveway, but she said she was instructed by Mr. Banfield to park her car in the cul-de-sac instead, in order not to scare off Ryan.

Days before the alleged double murder, the au pair also told Christine Banfield she was planning to take the family's child to the zoo the day of the planned meet-up. But Mr. Banfield's plan, she said on the stand, was to stay in her parked car and watch for when Ryan arrived.

Magalhaes testified Mr. Banfield had began leaving for work earlier and stopping at nearby restaurants for breakfast, to create a pattern because his plan was to wait at a nearby McDonald's until he was alerted Ryan had shown up to the home.

In the morning of Ryan's expected arrival, Magalhaes told prosecutors Brendan Banfield had Christine's cell phone, which he used to disable the home's automatic locks, before texting Ryan on Telegram to park in the driveway and walk in. After this, he turned off the phone and hid it in the kitchen.

The next part of the plan, according to Magalhaes, was for the au pair to call Christine's turned off phone when Ryan arrived, to make it appear she tried alerting her, before calling Brendan to say someone strange is coming into the home. Brendan then was to call Christine, to set up a record of the attempts to alert her.

When Brendan arrived, Magalhaes said they entered the home through the basement, and moved quietly upstairs to the main floor. At that point, she said Brendan made a hand gesture for her to be quiet and wait, moving upstairs to the bedroom after hearing a slapping sound.

They entered the bedroom, according to the au pair, and saw Ryan on top of Christine when Brendan yelled out he was a police officer. Magalhaes said Christine then yelled out, "Brendan, he has a knife!"

Magalhaes said Brendan shot Ryan in the head, and Christine told her to call 911. Magalhaes said she hung up immediately when Banfield gave her a hand gesture that looked like hanging up a phone.

Brendan Banfield then asked Magalhaes to go to the bathroom to get a towel. The au pair said when she handed him the towel, he began stabbing her in the neck.

"Brendan said, he yelled, 'Police officer!' Christine's first reaction - that was the first time I heard her say anything at that point - she yelled back at Brendan, 'Brendan, he has a knife!' That's when Brendan first shot Joe," Magalhaes said while recalling the day of the alleged double murder. "When I was bringing him the towel, he got on top of her, and that's when I first saw him stab her with a knife."

The prosecutor asked where Brendan Banfield was stabbing his wife, and Magalhaes said, "Her neck."

After this, Magalhaes recalled seeing Ryan moving, which is when she shot him in the chest. She testified Brendan Banfield was still stabbing Christine when she fired her gun.

Magalhaes said it was after this second gunshot when Banfield moved Ryan's body to get Christine's blood on his body.

This last portion of Magalhaes' testimony happened around 5 p.m., which is when the judge ended the day.

The prosecution is expected to continue questions Wednesday morning at 10.

Banfield's lawyer will have the chance to ask Magalhaes questions after the prosecution is finished.

John Carroll, who represents Brendan Banfield, spent the bulk of his opening statement challenging Magalhaes' credibility, pointing out how many times the prosecution offered her a plea deal she turned down before accepting her current one. He also said it was Joe Ryan, not Mr. Banfield, who killed Christine, but conceded his client and the au pair were having an affair.

The Fairfax County Commonwealth's Attorney's lead prosecutor on the case, Jenna Sands, focused her opening statement on the meticulous break-down of the alleged murder plot, while also stating their expert witnesses and blood evidence will confirm Magalhaes' testimony.

Before getting to Magalhaes, the prosecution called up five witnesses: a county official with access to the 911 call records, three officers who responded to the scene, and a medical examiner who conducted the autopsies.

The county official with 911 records confirmed there were three calls placed the morning of the alleged double murder. The first call sounded like a hang-up from Magalhaes' phone. The second call was placed by the 911 call center, but there was no answer. The third call was made by Magalhaes about 15 minutes after the first two calls.

In that third call, Magalhaes struggled breathing, and Brendan Banfield had to answer the operator's questions. Banfield can be heard saying he shot a man who was intruding, and that man stabbed his wife in the neck.

The officers who testified on the stand confirmed their body camera footage capturing their immediate response to the 911 call.

The defense focused his questions to the officers on Banfield's emotional state, which two of the officers responded by confirming he was having what appeared to be a panic attack at the home, and he later cried at the hospital when he was informed his wife died.

The judge in this case, Fairfax County Circuit Court Chief Judge Penney S. Azcarate is the same judge who presided over the Johnny Depp v. Amber Heard lawsuit.

"This judge tends to keep strict timelines and puts each side on a clock, so you have to be very careful how you use the time allotted to you. If you go over, then it's going to be done and you're not going to be able to continue with their witnesses," said Rahmani.

Former federal prosecutor John Fishwick, who previously served as U.S. Attorney for the Western District of Virginia before becoming the current owner of the Fishwick & Associates law firm, told 7News the prosecution will likely go through key points of this plot during Tuesday's opening statements.

"I think the prosecution's opening is going to be very meticulous. They're going to start with the relationship between the two of them - between Banfield and the au pair - that they had a romantic relationship, that they plotted this scheme that he was behind to kill both his wife and the man who showed up to have sexual relations with her, and they're going to say the au pair eventually has told the truth," Fishwick said.

Meanwhile, Fishwick said Banfield's lawyers are likely weighing a few approaches to his defense.

"I would expect the defense will go one of two ways. They're going to have to have an explanation for some things," Fishwick said. "Are they going to admit to certain things and say that he did not commit these murders? Or are they just going to go all in on reasonable doubt?"

TIMELINE | Alleged affair to murder trial: A timeline of events in Virginia's Brendan Banfield case

On Monday, both sides were able to whittle down a jury pool of 80 down to 16: nine men and seven women. Of the 16, four will be alternates.

Police found several photos of Brendan Banfield and Juliana Peres Magalhães in the Banfield home (Fairfax County Police Department)

The judge began Monday's jury selection process by asking potential jurors if they are available to serve on the jury for the four weeks the trial is expected to span, and if they knew anything about this case. More people were sent home from the first question, with the trial expected to continue through the first week of February.

Both the prosecution and defense then asked potential jurors if they had any experience with law enforcement or the criminal justice system, and if that would have an impact on their ability to remain fair and impartial. They also asked if they knew or were related to Banfield or his family, or anybody who worked on the case.

The prosecution then went through the list of 18 witnesses they plan to call to the stand, to ask if the potential jurors knew or were related to them. Most of the witnesses are law enforcement officers or first responders working directly on the case.

Juliana Peres Magalhaes, the au pair with whom Banfield was having an affair, has agreed to testify as part of a plea deal she accepted. In exchange for her testimony, she will plead to the lesser charge of manslaughter and walk free because of the time she already served, before being deported to Brazil.

Nobody raised their hands when asked if they knew or were related to anybody involved in this case.

Banfield's lawyers asked if any of the potential jurors, or anybody they knew, was involved in an extramarital affair. This question immediately disqualified one person, and a few others who raised their hand to this question were eventually left off the jury.

Magalhaes' testimony is expected to continue 10 a.m. Wednesday, with the trial expecting to last four weeks - until February 6. However, it can go a little bit longer if the jury is still deliberating.