The case involving former cardiologist Guy Turcotte was supposed to begin today but has been put off until November because new information has emerged.
Turcotte, whose case shocked and angered Quebecers, denied intent but admitted to causing the deaths of his two children in their beds in 2009.
He stabbed his son, Olivier, and daughter, Anne-Sophie, a total of 46 times.
The Crown had charged him with two counts of first-degree murder, but a jury found him not criminally responsible for the deaths.
Turcotte will be detained until November.