MONTREAL - A mysterious letter has postponed a mental-health hearing for a former doctor who stabbed his children to death and was found not criminally responsible by a jury.

Guy Turcotte was scheduled to appear Friday before a mental health review board that will decide whether to let him go free -- but the hearing was put off until November.

Quebecers had been riveted by the ex-cardiologist's murder case and there was widespread outrage last month following the trial verdict. Friday's highly anticipated review-board hearing was top news in the province.

But the five-member panel hearing the case demanded more time to investigate. Lawyer Medard Saucier, chairman of the tribunal, said the letter dated Aug. 10 was received Thursday by the panel.

"It was a letter that contained some information -- relevant, at first look, to the hearing," said Jean-Claude Hebert, a lawyer who is acting as spokesperson for the board.

The lawyers were informed Friday of the new information and agreed to postpone the case even though the new date -- Nov. 4 -- surpasses the 90-day time frame following a verdict within which a hearing has to take place.

Details about the nature of the letter, who it came from, and its contents were being closely guarded.

In the meantime, Turcotte will remain detained at the hospital. He agreed through his lawyer to the delay.

"He will have to stay in detention until the very moment the board will deliver its decision," Hebert said.

Turcotte's mother and father were among a contingent of family present for Friday's hearing. On the other side, only the victims' grandmother -- Turcotte's ex-mother-in-law -- was present.

The hearing was to be held under tight security at a Montreal psychiatric facility.

In his sensational murder trial, Turcotte admitted to causing the deaths of his two children in their beds in 2009 -- but he denied intending to do it.

He stabbed his son, Olivier, and daughter, Anne-Sophie, a total of 46 times. But Turcotte said he could only remember flashes of that fateful evening, devastated as he was by grief upon learning that his estranged wife had been cheating on him.

The Crown had charged him with two counts of first-degree murder, but a jury found him not criminally responsible for the deaths.

The panel will eventually decide whether Turcotte should obtain his conditional release, receive an unconditional release, or remain detained in a psychiatric institution.