A lawyer for Brian Walshe said during opening statements Monday morning that Ana Walshe’s death in January 2023 was a result of a “sudden unexplained death.” Brian Walshe is on trial for first-degree murder after the disappearance of his wife.

Larry Tipton, the defense attorney, said that at about 2:30 a.m. on New Year’s Day 2023, Brian Walshe found his wife in bed and “sensed something was wrong.”

“You will hear evidence that it made no sense to him, but he nudged Ana, his wife,” Tipton said. “She didn’t respond. He nudged her again, a little harder. She didn’t respond. He nudged her now in a frantic and panicked reaction to where she actually rolled off the bed.”

Earlier that night, Brian Walshe had enjoyed a dinner with his wife and a family friend, and the friend left the home between 1 a.m. and 1:30 a.m.

About an hour later, Brian Walshe discovered his wife had suddenly died in bed, according to Tipton — a sharp contrast to the prosecution’s theory that Brian Walshe killed his wife.

“You will hear evidence in this case of sudden, unexplained death,” Tipton said. “Sudden unexplained death is known within the medical community and forensic community, but it is, to this day, not well understood … One hour he’s with her, he cleans the kitchen, he comes back up and she is dead.”

The explanation offered by Tipton on Monday followed the prosecution’s presentation of their theory of the case, one of a husband convicted of federal art fraud and the possibility of paying $400,000 in restitution and prison time hanging over his head.

Ana WalshePolice continue looking for missing Cohasset woman Ana Walshe.What did prosecutors say?

Prosecutors on Monday gave a detailed account of the search for Ana Walshe nearly three years ago.

A coworker of Ana Walshe’s who worked at the international real estate firm Tishman Speyer in Washington, D.C., learned on Jan. 4, 2023, that the Massachusetts woman was missing, according to Norfolk Assistant District Attorney Gregory Connor.

Theresa Marchese, the coworker at Tishman Speyer, spoke with Brian Walshe that morning. He spoke calmly and told her that Ana Walshe left for a “work emergency” on New Year’s Day and flew down to Washington, D.C.

Marchese then drove to Ana Walshe’s townhouse, and on the way, Marchese spoke with Brian Walshe again to get the combination for her garage. When Marchese arrived, there was no car, no Ana Walshe. She couldn’t get into the apartment because it was locked.

The real estate company’s global head of security and retired Secret Service agent, Hugh Dunleavy, got involved. Brian Walshe got very upset after receiving a call from Dunleavy, the prosecutor said, and he repeated that Ana Walshe left for the nation’s capital due to a work emergency.

Ana WalshePolice continue looking for missing Cohasset woman Ana Walshe. Walshe and her husband, Brian, pose for a photo.

Dunleavy eventually called Cohasset police later that day, and reported her missing — the first person to alert police just before noon on Jan. 4, 2023.

The trial is expected to last two to three weeks, and Connor said evidence will include photos of the family home on Chief Justice Highway in Cohasset, videos from different stores, Ana Walshe’s bank records, a hatchet and a hacksaw.

Ana Walshe was 39 when she went missing. A Serbian immigrant, she began working in real estate and in February 2022 got her dream job at Tishman Speyer. She bought a townhouse in Washington, D.C., and expected her family to move down as well.

Brian Walshe previously pleaded guilty to a count of fraud in federal court and was awaiting sentencing at the time of her disappearance.

The family was delayed moving down to Washington, D.C., due to Brian Walshe’s pending sentencing in a federal fraud case he pleaded guilty to.

He was accused of owing more than $400,000 in restitution, and he later told investigators that the fraud case had caused a strain on their marriage.

Prosecutors plan on presenting digital evidence of Google searches about divorce, how to dispose of body parts after a murder and about accessing a credit card for a missing person, among other similar searches.

Prosecutors also plan on presenting surveillance footage evidence that shows Brian Walshe purchased cleaning supplies, a hazmat suit, cutting instruments such as shears and a hacksaw from various stores.

Police recovered a trash compactor near Brian Walshe’s mother’s apartment in Swampscott, where they found boots, a black coat, a vaccination card belonging to Ana Walshe, a hazmat suit, rugs, a hammer, hatchet and hacksaw, according to Connor.

Some of those items contained DNA belonging to both Brian Walshe and Ana Walshe, Connor said.

“Use your common sense,” Connor told jurors. “At the end of this trial, we will speak to you one more time. It is at that time we will ask that you find the defendant guilty of murdering his wife with deliberate premeditation.”

Brian Walshe stands accused by Norfolk County officials of killing and dismembering his wife, Ana Walshe, in January 2023. Investigators say Brian Walshe suspected his wife was having an affair and that he killed her amid financial uncertainties after being convicted of federal fraud charges.

Brian Walshe, who lived in Cohasset with Ana Walshe, 39, and their three children, pleaded guilty to the counts of witness intimidation (misleading a police investigation) as well as disinterment of a body at the start of jury selection earlier this month.

The trial continues Monday with the first witness, an investigator with the Cohasset Police Department.