The judge in the Summer Hope case has agreed to consider an application from the defence lawyer.
The lawyer for Jonathon Hope took the unusual step, last week, of submitting an application to find the father not criminally responsible.
Jonathon Hope and Lisa Guerin were convicted of failing to provide the necessities of life to their 16-month-old daughter who died after drinking Hope's methadone.
On Thursday, Hope's lawyer argued her client was suffering from a brain injury when his daughter drank the methadone and died.
Joan Blumer says Hope was suffering from profound memory deficit, disorganized thought patterns, and mood disability. She also says a proper mental assessment was not done when Hope was originally found fit to stand trial.
The Crown still needs to present its arguments on the application but says the defence should have made more of Hope's mental state during the trial.
Ken McCaffery says it's too late to suggest now that Hope did not understand the consequences of his inaction.
McCaffery will argue his points on Monday, but says if the judge's decision could break new legal ground.
"Normally this issue is tried as part of the trial, or even tried as [part of the main defence]. So I agree that he may have to set a new test and in that case it may be a precedent setting decision," says McCaffery.
