A psychologist who met with Lindsay Clancy days after she killed her children has revealed new details about the moment when she claimed a voice told her to do it.

It was day 15 of the mom-of-three's murder trial inside Plymouth County Superior Court, Massachusetts, on Tuesday, when her claim of postpartum psychosis took center stage.

The 36-year-old former nurse is charged with three counts of first-degree murder in the killings of her three children, Cora, five, Dawson, three, and eight-month-old Callan, inside the family home in Duxbury, Massachusetts, on January 24, 2023.

Clancy strangled the children with exercise bands in the basement of the home before cutting her wrists and neck and jumping from a second-floor bedroom window in an attempt to kill herself. She survived but was left paralyzed from the waist down.

Clancy has admitted to killing her children but has pleaded not guilty by reason of insanity, claiming that she was suffering from severe postpartum psychosis and depression at the time.

Inside the courtroom on Tuesday, jurors heard testimony about the moment that Clancy first told her then-husband Patrick Clancy that she had heard a voice.

Dr Paul Zeizel, a highly experienced, well-respected forensic psychologist who works with Clancy's defense attorney Kevin Reddington, testified that he visited Clancy at Brigham and Women’s Hospital days after the killings.

He first visited her on February 4, 2023 - 11 days on from the killings - at Reddington's request because the defense attorney had taken on her case and was concerned about her mental health and the fact that she had been allowed no visitors.

Dr Paul Zeizel recalled the moment Lindsay Clancy told her husband about the 'male voice' in her head that ordered her to kill her children and herself

Clancy, 36, is on trial for killing her three children, Cora, five, Dawson, three, and eight-month-old Callan, at her home in Duxbury, Massachusetts , in 2023

Dr Zeizel testified that he had to get a court order to be able to enter Clancy's hospital room, where he found her handcuffed to the bed.

Clancy had only just had a breathing tube removed and had been on a lot of medication, so was 'foggy.'

'She didn’t know where she was. She wasn’t sure what time it was. She knew who she was,' he recalled. 'She remembered what had happened but was very foggy.'

Clancy asked him if she could use his cell phone to call Patrick, who she had not seen or spoken to since that tragic evening.

Dr Zeizel let her, so long as the call was on speakerphone.

Clancy called Patrick but he did not pick up.

Two days later, when Dr Zeizel visited again, Clancy called again from her hospital bed. That time Patrick picked up.

It was during that call that Clancy told her husband that a man's voice had commanded her to kill the children and herself.

‘She had said that she heard a male voice ordering her, telling her that she didn’t have any choice, but she had to kill her children and then kill herself,’ Dr Zeizel testified.

In the call, Clancy also told Patrick 'that she loved him very much,' he testified.

Patrick had previously testified about the phone call when he took the stand on the opening days of the trial.

When Reddington asked the psychologist if he told Clancy to claim to have heard voices, Dr Zeizel insisted 'absolutely not.' He said he had let her call her husband 'out of human compassion.'

Zeizel testified that he visited Clancy in hospital in the days after the killings. She borrowed his phone to call her husband, Patrick

Dr Zeizel's testimony comes days after an explosive moment in the courtroom where a police officer admitted the state had pursued a theory that the doctor coached Clancy to claim that she killed her children because she was hearing voices.

Prosecutors have repeatedly raised questions about when Clancy first mentioned hearing voices.

And, during a tense cross-examination from Reddington last week, Massachusetts State Police Sgt Dan Lawlor was forced to admit that investigators discussed a ‘theory’ that the psychologist had planted the seed in Clancy’s mind after the killings.

The officer then also admitted that there was no evidence to support the theory - marking a blow to the state’s case.

Clancy's assertion that she was commanded by a voice to kill herself and her children is a crucial element of the defense's case - arguing that she was suffered auditory hallucinations from postpartum psychosis.

Prosecutors, meanwhile, argue that she was of sound mind and planned the killings, calling several friends, family members and medical professionals to the stand to testify that Clancy never told them she was hearing voices prior to the killings.

Dr Zeizel has met with Clancy over 45 times, many of them inside Tewksbury Hospital where she continues to receive treatment.

He testified that his mental health evaluation of Clancy found her to be an honest patient.

He also described how psychotic episodes can come and go.

'People with psychoses have intermittent symptoms. They can be fine one day. Then the next day they can be hearing voices, seeing things, smelling things,' he testified.

'Hallucinations are like waves at a beach. They come and go.'

People in the grips of psychosis can also appear competent to people, such as being able to make phone calls and driving, he testified.

Cora and Dawson Clancy building a snowman with their mother on the day of the killings

On Tuesday, the first full day of the defense's case, jurors also heard from Patrick's mother Sue Clancy.

She testified that her former daughter-in-law was a loving mother who was 'begging for help' for her postpartum mental health issues in the months leading up to the killings.

In a stunning moment, prosecutor Shanan Buckingham also confronted the grief-stricken grandmother about whether or not she agrees that murder is a 'mortal sin' as a practicing Catholic.

'You’re aware that murder is considered a mortal sin?' she asked.

Reddington quickly objected and Judge William Sullivan ordered the two sides to the bench.

He then instructed the jury to dismiss that comment and struck it from the record.

Throughout the day, jurors also heard from other defense experts.

Dr Elizabeth Laposta testified that Clancy's injuries reveal she jumped head-first out of the window that evening, landing on her head on the frozen ground.

Her testimony pushed back on the prosecution's attempts to cast doubts on Clancy’s suicide attempt, suggesting that bloodstains on the shingles of the home suggest she clung to the window ledge and dropped rather than jumping out of the window.

Dr Zeizel will return to the stand on Wednesday morning.

If convicted of murder, Clancy will be sentenced to life in prison without parole.

If found not guilty by reason of insanity, she will be sent to a psychiatric hospital where she could be released in future if she is deemed not to be a danger.