A suburban Washington, D.C. man who was having an affair with his family's Brazilian au pair used an elaborate scheme to lure an unsuspecting man to the house as part of a plan to kill his wife, prosecutors said in opening statements on Tuesday.

Brendan Banfield is charged with aggravated murder in the 2023 killings of Christine Banfield and the second man, Joseph Ryan, at the Banfields' home in northern Virginia. He has pleaded not guilty and could face life in prison if convicted.

Juliana Peres Magalhães testified on Tuesday that she began working as an au pair in the home in October 2021, when she would have been 21 years old. She and Brendan Banfield began a sexual relationship about 10 months later. Banfield told her he wanted to marry her and have children with her, but he needed to "get rid of" his wife first, she testified. He didn't want to divorce his wife because "she would have more money than he would" and because he wanted custody of the couple's 4-year-old daughter.

Banfield came up with a plan to create a fake profile for his wife on a sexual fetish site, Magalhães said. Magalhães and Brendan would both post to the site from Christine Banfield's laptop, and they were careful to post only when Christine Banfield was home, Magalhães said.

"He knew that we needed to have some alibis," she testified.

In opening statements, Chief Deputy Commonwealth's Attorney Jenna Sands told jurors that Banfield and Magalhães spent a month arranging an elaborate scenario with Ryan in which Ryan would act out an arranged rape fantasy. They agreed that Ryan would come on the morning of Feb. 24, 2023, while Christine Banfield was sleeping, and bring restraints and a knife, Sands said.

"He thought Christine was a terrible mother," Sands said, according to CBS affiliate WUSA-TV. "He wanted her out of the picture."

In preparation, both Magalhães and Brendan Banfield traded in their phones in an effort to hide evidence. He also changed the windows in the home to improve the soundproofing and checked neighbors' homes to see who had doorbell cameras, Magalhães said.

On the morning of the killings, Magalhães left the home with the child and waited in her car for Ryan to arrive. Brendan Banfield had left earlier and was waiting at a nearby McDonald's for her to call. When she did, he returned home. The pair took the child to the basement and went upstairs to find Ryan on top of Christine Banfield, who was on the floor.

"When I got to the bedroom, he yelled, 'Police officer,'" Magalhães said of Brendan Banfield. "Christine yelled back at Brendan, saying, 'Brendan! He has a knife!' That's when Brendan first shot Joe."

Christine Banfield told Magalhães to call 911. She did, but then hung up after Brendan Banfield motioned to her, she said. She went to the bathroom for towels, and when she returned, she saw Brendan Banfield stabbing his wife, she said. She was alternately pacing and squatting down, covering her eyes, but at some point she saw Ryan moving and shot him with a gun that Brendan Banfield had given her that morning, she testified. After that, she called 911 again when Brendan Banfield gave the OK, she said.

Brendan Banfield appeared to cry in court Tuesday while listening to the 911 call from the day his wife was killed in their bed, WUSA-TV reported. 

Magalhães was also charged with murder but pleaded guilty to a lesser charge of manslaughter in 2024 after cooperating with investigators. She will be sentenced at the conclusion of Banfield's trial.

Banfield's attorney, John Carroll, said in opening statements that Magalhães had maintained her innocence for a year but eventually changed her story in exchange for a sweetheart deal.

"The whole reason she was arrested was to flip her against my client," Carroll said.

The prosecution's theory relies on the idea that Banfield and Magalhães were "catfishing" Ryan by pretending to be Christine Banfield. However, the lead homicide detective and the forensic detective both disagreed with that theory, Carroll said. Both were later transferred. Carroll said there was "turmoil" inside the police department over that case that some media have dubbed the "au pair affair."

"You're going to see a presentation of a horrible, tragic, awful event," Carroll said. He said there is no dispute that Banfield and Magalhães were having an affair; however, "there's an awful lot more to look for."

Banfield, whose daughter was at the house on the morning of the killings, is also charged with child abuse and felony child cruelty in connection with the case. He will also face those charges during the aggravated murder trial.

Joseph Ryan's mother, Deirdre Fisher, told WUSA-TV that her son had talked to her about consensual role play but he was not a violent person. Fisher told the station she remembers every detail of learning about her son's death.

"I remember when I got the call from the detective … I could hear my own voice screaming," she said. "It was almost like it was outside of my body hearing that he had been killed."