The judge in the trial of Lindsay Clancy, the Massachusetts mother accused of killing her three young children, has declared a mistrial after the jury could not reach a unanimous verdict and remained deadlocked after a week of deliberations.

Jurors in Plymouth state court spent more than 38 hours in deliberations over the charges against the 36-year-old mom, which came on the heels of a weeks-long trial that directed national attention to maternal mental health issues that can occur postpartum.

The 12-person jury was made up of nine women and three men and, according to the notes given to the court, was split 11 to one.

After the jury returned without a verdict for the third time, Judge William Sullivan declared a mistrial but was interrupted by a last-minute request from Clancy's lead defense attorney, Kevin Reddington, who requested one hour to petition for an emergency stay to seek relief from a superior court judge.

That emergency filing with the Massachusetts supreme judicial court asked a single justice to order Sullivan to further question the juror arguing the juror was "biased" and, per jury notes, unwilling to follow the court's instructions on reasonable doubt.

"Intervention is necessary in this case to avoid an avoidable mistrial of a case that is so time and labor intensive and that has captured so much public attention," the filing reads, which also claimed that the court had "abdicated its responsibility to ensure the integrity of the jury".

The filing also asked that the juror be barred from further deliberations if Sullivan determined that they could not follow the instructions issued by the court.

"A mistrial at this point is entirely avoidable, but only if the court does its job," the filing says.

Additionally, the filing claimed the court "reflects a bias against those who suffer from debilitating mental illness", arguing that mental illness is a "protected category" under the fifth and 14th amendments of the US constitution.

The filing was discussed with the Massachusetts supreme court justice Dalila Argaez Wendlandt during a Zoom hearing that was open to the public for viewing. Prosecutor Jennifer Sprague summarized what happened with the jury and their repeated notes indicating a deadlock before defense attorney Dana Goldblatt argued that the supreme judicial court had the discretion to order the trial court to make the inquiry of the juror. Wendlandt then said she would take the matter under advisement.

The petition was subsequently denied.

Clancy, a former neonatal and delivery nurse, had been accused of strangling her three children, Cora, five, Dawson, three, and Callan, eight months, in the family's Duxbury home in January 2023.

Prosecutors argued in opening statements that Clancy had "coldly and efficiently executed" her children, doing so with "no hesitation, with deliberate premeditation and extreme atrocity and cruelty" after she "drew her husband out of the house, their father, so that she had the opportunity and the time to carry out these murders".

But Clancy's defense team argued she was "suffering from psychosis" when she killed her children and allegedly attempted suicide by jumping from an upper window in her home, which left her partly paralyzed. Reddington told jurors that Clancy suffered from postpartum depression after giving birth to her third child, Callan, and been prescribed a cocktail of medications.

"This is a young woman who, with her husband, tried very hard to get the help she needed," he said.

Clancy has not denied that she had killed her children but her not guilty plea was predicated on a lack of criminal responsibility because, as her defense team said, she was suffering from postpartum psychosis, which included auditory hallucinations that commanded her to harm her children, and undiagnosed bipolar disorder.

Under Massachusetts law, the defendant must have "retained the substantial capacity to appreciate the wrongfulness or criminality of their conduct and to conform their conduct to the requirements of the law" in order to be found guilty.

Throughout the trial, jurors heard from Clancy's former husband Patrick Clancy, her mother and aunt, and an array of psychologists and treating physicians. The court heard that Clancy had been prescribed 13 different medications for anxiety and sleep, which the defense said may have exacerbated her symptoms of depression.

Clancy had checked herself into psychiatric clinic in the weeks before the killings. Later, on 24 January 2023, she had sent her then husband out for food and to collect pharmacy medications. In that time, police say she strangled their children with exercise bands. Her ability to orchestrate a window of time to carry out the killings, prosecutors argued, was evidence of premeditation.

Before resting his case last week, Reddington called forensic psychiatrist Dr Phillip Resnick to testify that Clancy had "severe depression" and a history of anxiety, which increased after the birth of her children to the point that she "felt she couldn't function".

"At the time of the crime on Jan 24, 2023, Ms Clancy was frankly psychotic," Resnick said. "She was clearly psychotic on that day."

After the declaration of Clancy's mistrial, prosecutors have the option of trying her again. The court has set a status conference for 9am ET on 29 September.

Clancy's criminal trial will be followed by a civil claim brought by both Lindsay and Patrick Clancy against her medical and mental healthcare providers. The former couple claim the providers committed medical malpractice by failing to properly diagnose, treat and monitor her severe postpartum psychiatric condition.

After formally declaring the mistrial, the judge thanked the jury for their time and consideration.

"Each one of you knew how long the case was going to go. You knew how difficult the case was going to be to listen to facts-wise, but still, you braced for that duty," Sullivan said before dismissing them.

He also indicated that should there be a re-trial, he would want it to happen "sometime in the fall".

Plymouth county district attorney Tim Cruz told reporters that Clancy's had been "an emotional trial for everybody".

"This was and has always been about getting justice for those three little babies," Cruz said. "We're here at this courthouse today because those children are not. Our priority has always been to fight for Cora, for Dawson and for Callan."

Cruz also praised assistant district attorneys Jennifer Sprague and Shanan Buckingham, who he said "are both mothers themselves – and went home to their families after each long day in court".

Reddington addressed reporters outside the courthouse, too, saying that Cruz "knows he was crushed".

"I'm representing a woman who is a fantastic, wonderful individual," Reddington said. "This woman is so brave, so awesome. She sat there through seven weeks of the trial, where nobody had anything bad to say about her except the two prosecutors."

Reddington also thanked the jury, "minus one" – referring to the holdout juror who he says he "hope[s] they can sleep at night".

In response to how Clancy's parents are doing after the mistrial, Reddington said: "Not good."

"They know that they were robbed by one [juror] for whatever [their] agenda was," Reddington remarked. "And I got a funny feeling that [the jury] would have gone on for another week if they had to. So I hope that [juror] can sleep well at night."

"If we didn't have that one individual, we would've had a verdict and we would be out of here," he continued. He added that Clancy is "like a a daughter to me".

It was not immediately known for what outcome the 11 decided jurors had voted.

Donald Trump also weighed in on the trial, telling reporters at the White House that the case was a "horrible tragedy" and a "terrible situation".

"I assume there's going to be another trial," the president said. "She did a horrible, horrible thing. Can't be worse.

"There'll be a price. It's going to be a mental institution or jail or something ... It's too bad."