Holly Hamilton's friends and family gasped, and some broke down in tears, as a judge declared a mistrial in the case of the ex-boyfriend charged with stabbing her to death.

As many as 50 supporters sat in Hamilton superior court Friday. It was supposed to be the first day in the second-degree murder trial of Justin Dumpfrey, who has pleaded not guilty. But the trial abruptly ended, and lawyers will meet Monday to set a new date.

Justice Paul Sweeny ordered a publication ban around the reasons for the mistrial.

Hamilton was stabbed 17 times, the court heard, on the evening of Jan. 14, 2018. The 29-year-old single mom was missing for two days before her body was found locked in the trunk of her work vehicle. Hamilton was last seen leaving the Upper Wentworth-area townhome she shared with her sister. She had a four-year-old daughter with Dumpfrey, and the little girl also lived there.

Dumpfrey (left) is seen here alongside Hamilton. (Facebook)

On Jan. 15, the court heard, Dumpfrey dropped off the little girl at Hamilton's mom's house, rang the doorbell and walked away when someone answered the door. The little girl had new toys, and wore a different coat from the day before.

Hamilton's murder drew attention from those fighting gender-based violence. It became the focus of a women's march at city hall, and a would-be search party on Jan. 16 became a vigil outside Dumpfrey's Barton Street apartment.

Police said then that there was a history of violence between Hamilton and Dumpfrey.

The defence attorney is John Erickson.