Was Ana Walshe murdered by her husband? Or did she die in bed of a mysterious, unexplained medical event?

Defense attorneys for her husband, Brian Walshe, will try to convince jurors of the latter, one said in opening statements Monday as his murder trial began in earnest, almost three years after Ana vanished from a Boston suburb in the early hours of New Year’s Day 2023.

It was the first time anyone has publicly offered a theory for the cause of Ana’s death since Walshe was charged with her murder. Her body has never been found, and while Walshe two weeks ago pleaded guilty to illegally disposing of Ana’s body and misleading police as they investigated her disappearance, he insists he did not kill her.

Walshe faces life in prison without the possibility of parole if convicted of first-degree murder for Ana’s death.

Here’s what happened Monday during opening statements and the first day of witness testimony:

Prosecutors have told the jury they will prove Walshe planned to kill his wife. But in opening statements Monday, Assistant District Attorney Greg Connor instead walked the panel through the known events in the days around Ana Walshe’s disappearance – without suggesting how Walshe allegedly killed her.

After surprise guilty plea to lesser charges, Brian Walshe goes on trial for wife’s murder

Ana Walshe flew to Massachusetts on December 30, 2022, from Washington, DC, where she worked as a real estate manager for Tishman Speyer. The next day, the Walshe family hosted Ana’s former boss, who joined them to celebrate New Year’s Eve.

That man is expected to testify at trial that he left the Walshe home after 1 a.m. on January 1, 2023, and that the couple seemed happy.

“When he left, she was home, she was alive, she was with her husband. No one has seen her since her husband said she left on January 1,” the prosecutor said. “She has not accessed her finances, her email, her phone has made no calls and no one has found her body.”