Lindsay Clancy holdout juror had no doubt she deliberately killed her children

Paula Devlin, one of the other jurors, told CBS Mornings that the panel had spent several days trying to convince Desronvil to change his mind.

“We all worked together to convince ourselves once we got to that point where it was 10 to 2,” she said.

The jury foreperson, a retired fifth-grade teacher, described not being able to reach a verdict as “awful” and an “emotional rollercoaster”.

She told NBC that Desronvil had “admitted he had reasonable doubt”, but as she started filling out the verdict sheets, he apparently said: “But I’m still not going to say that she’s not guilty by reason of insanity.”

Another juror told local CBS station WBZ-TV that most of the jurors had been “very firm in their stance” from the start and “the stand-alone juror was not the only one that was unwilling to see things from the other side”.

But they added that because Desronvil would not “follow” his reasonable doubt nor offer logical reasoning for his position, they felt Clancy had not received a fair trial.

The identities of all 11 jurors have not been officially disclosed but in the US, once a case is over, any juror can choose to speak publicly about a case and their deliberations.

Patrick Clancy, the children’s father and Lindsay Clancy’s ex-husband, is due to speak publicly about the case in an interview with the CBS programme 60 Minutes on Sunday.

In it, he is expected to discuss his grief, his memories of his children and the conspiracy theories that have flooded social media since the trial began.

He said he still speaks to his children “all the time”, describing it as “a way I stay connected to them”.

During the trial, Clancy’s defence team had attempted to use her being put on more than a dozen medications in the lead-up to the killings, as well as seeking help from a suicide hotline and an emergency room, as evidence of her psychosis.

Postpartum psychosis can involve hallucinations and delusions, and her lawyers argued that she was unable to understand the nature of her actions or distinguish right from wrong.

A forensic psychiatrist who testified for the defence said Clancy experienced a “command hallucination” and a “delusion of influence” when she killed her children.

However, her psychiatrist testified for the prosecution that Clancy did not show signs of psychosis during their sessions, while another psychiatrist noted that the condition was not currently recognised by the American Psychiatric Association.

Under Massachusetts law, prosecutors had to prove beyond any reasonable doubt that Clancy was criminally responsible for the jury to find her guilty. The defence did not have to prove her mental illness or lack of criminal responsibility.

The mistrial leaves the case unresolved. Prosecutors have not said whether they will seek a retrial.

Clancy’s lawyer, Kevin Reddington, has said he hopes to reach an agreement with prosecutors to avoid a second trial.

He told ABC’s Good Morning America that he was upset that the lone juror would not acquit Clancy.

He said the holdout “would not apply the law of reasonable doubt” as instructed by the judge, adding: “That’s not right. And that’s why I was upset.”

The next court hearing is scheduled for 29 September at Plymouth Superior Court in Massachusetts.