Opening statements are expected to begin Tuesday in the trial of Brendan Banfield, a former IRS special agent who is accused of orchestrating a grisly double murder to conceal an affair with his family’s au pair.

Twelve jurors and four alternates were seated Monday as the trial begins, FOX 5 reported.

Banfield is charged with aggravated murder in the February 2023 killings of Christine Banfield and Joseph Ryan at the Banfields’ home in the idyllic Washington, D.C., suburb of Herndon, Virginia.

According to court records, Banfield and then-22-year-old Brazilian au pair Juliana Peres Magalhães were present when his wife and Ryan were killed in the home’s primary bedroom. At the time, the au pair told investigators they had discovered Ryan — a stranger — stabbing Banfield’s wife and had both opened fire to stop the intruder.

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Prosecutors, however, allege a more calculated plot. They say that Banfield and Magalhães lured Ryan to the house and staged the scene to make the homicides appear like an act of self-defense.

Prosecutors have said Banfield was impersonating his wife, Christine, in an online account on a fetish website. Prosecutors said the husband lured Ryan to the couple’s Herndon-area home as part of his plot to kill his wife.

“It is a theory in search of facts rather than a series of facts supporting a theory,” John Carroll, Banfield’s attorney, previously said.

VIRGINIA AU PAIR MURDER: FETISH PLOT, AFFAIR, GUN RANGE TIED TO DOUBLE HOMICIDE AT HOME, PROSECUTORS REVEAL

When police initially responded to a 911 call from the residence in February 2023, they found Christine with stab wounds to the neck and Ryan with fatal gunshot wounds in the upstairs bedroom of the home.

Authorities took Christine to the hospital, where she was later pronounced dead, Fairfax County Police Department Chief Kevin Davis said. Officials recovered a knife and two guns from the scene.

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Banfield has pleaded not guilty in the case, but Magalhães, a Brazilian national, pleaded guilty to manslaughter in late 2024.

She is expected to testify against Banfield during the trial and provide a first-hand account of the alleged plot.

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If convicted, Banfield is expected to face life in prison. Fox News Digital has reached out to Banfield’s attorney, John Carroll, for comment.

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The trial is expected to last four weeks. Court sessions will begin at 10 a.m. each day and run Monday through Thursday, according to court administrators.

Fox News Digital’s Audrey Conklin and the Associated Press contributed to this report.