Prosecutors in the closely watched case alleged that on 24 January 2023, Clancy intentionally strangled all of her children – Cora, 5, Dawson, 3, and Callan, eight months – in their Duxbury, Massachusetts, home.
After weeks of emotional testimony, the jury took a week to deliberate, repeatedly telling the judge that they could not reach a verdict.
The deadlocked stemmed from a lone juror who voted to convict Clancy of first-degree murder, while the 11 other jurors intended to acquit Clancy by reason of insanity.
In Massachusetts, as well as in all US criminal murder trials, juries must reach a unanimous decision to convict or acquit a defendant.
Because the jurors failed to unanimously agree on whether the prosecution had proved Clancy was guilty “beyond a reasonable doubt” as required by US law, the judge declared a mistrial on 4 September, which means that she was neither found guilty nor not guilty.
Clancy is currently being housed in a state-run psychiatric hospital and medical facility in Massachusetts.
Ana Faguy contributed reporting.