A psychologist testified about the first words Lindsay Clancy spoke to her husband—and subsequently, the defense moved for a mistrial. The five words he uttered in court were…

Dr. Kirk Heilbrun; Lindsay Clancy.Credit : Greg Derr/The Patriot Ledger via AP, Pool

Prosecutors in the Lindsay Clancy case called their second rebuttal witness Monday, Aug. 24, a forensic psychologist who testified about Clancy’s mental state and possible reasons for why she killed her three children.

Clancy, 36, is charged with the murders of her children, Cora, 5, Dawson, 3, and 8-month-old Callan, whom she strangled to death with exercise bands at the family’s home in Duxbury, Mass., in January 2023.

She has pleaded not guilty by lack of criminal responsibility and her defense hinges on the argument that she had postpartum psychosis.

The proceedings have been live-streamed by the Associated Press.

Dr. Kirk Heilbrun, who evaluated Clancy over three days in April 2026, took the stand in Plymouth, Mass., to discuss his findings. He told the court he diagnosed Clancy with Bipolar II disorder, but said she had not experienced manic episodes. He testified that she experienced depressive episodes and said the diagnosis was difficult to reach, but noted that she has responded well to medications used to treat the condition.

During his testimony, Heilbrun described Clancy’s “intrusive thoughts,” including that her “brain is damaged” and that she needed to “kill herself” and harm her children.

Heilbrun also evaluated Clancy’s criminal responsibility and discussed two possible reasons for the killings, which he described as “so out of character” for her.

According to Heilbrun’s testimony, Clancy either believed she needed to kill her children so they would not suffer after her death or was experiencing acute psychosis, the latter of which he ultimately ruled out.

Heilbrun pointed to Clancy’s response when her then-husband Patrick returned home and found her injured and their children dead. When Patrick asked what she had done, Clancy told him, “I tried to kill myself.” Heilbrun said that response was inconsistent with psychosis, saying someone experiencing hallucinations might instead have said, “I did what I had to do” or “I did what the voice said.”

The psychologist told the court Clancy reported hearing a male voice for the first and only time during the roughly 18 minutes the killings occurred, telling her, “This is your last chance. You have to kill the kids so you can kill yourself.” He called the timing unusual and said it could be a way to lessen her culpability. Heilbrun added that Clancy gave “inconsistent” accounts of what the voice instructed her to do.

Heilbrun also testified that Clancy killed her children as part of what he described as “altruistic filicide,” saying she believed they would suffer without her and that killing them would allow them to be “together in heaven.” As she killed them, she told the children, “Go to God, baby. Go to God,” the psychologist said.

But Heilbrun’s testimony was cut short Monday after he mentioned Clancy’s Catholic faith in one of his later responses. Clancy’s attorney Kevin Reddington then moved for a mistrial, arguing that her religion had been repeatedly brought up in witnesses testimony despite being irrelevant to the case. The prosecution said that was not their intent.

Judge William Sullivan denied Reddington’s request for a mistrial but instructed prosecutors to address the issue with their witness. He said he planned to tell jurors that Heilbrun’s understanding of the Catholic religion is an “inappropriate area of inquiry.”

“The religion that the defendant was raised with is absolutely an inappropriate area of testimony,” Sullivan told the jury when they returned to the courtroom.. “It is to be stricken. It is not to be considered. I can’t be any more clear of that. It cannot be considered.”

The jury was subsequently dismissed, with Heilbrun expected to resume his direct testimony Tuesday, Aug. 25.

Prosecutors are expected to call one more rebuttal witness before closing arguments this week.