On the last day of a disturbing second-degree murder trial for a mother charged with killing her two young sons, lawyers from both sides spent the morning entering their closing arguments.

Allyson McConnell's defence lawyer Peter Royal gave his argument first, saying the court's job is a ‘heavy one', and that ‘you couldn't imagine a sadder case than this.'

He added, "[The] Crown's burden is a heavy one for a very good reason, we don't want to convict someone who is probably guilty."

The Crown alleges the deaths were an act of revenge against her estranged husband.

The trial stems from the deaths of McConnell's two sons in the bathtub of the family home in February 2010.

McConnell had since admitted to drowning 2-year-old Connor and 10-month-old Jayden – but pleaded not-guilty to second-degree murder charges in the case.

Closing arguments ended late Thursday morning, the judge is expected to give a decision on April 20.

With files from Serena Mah