The fate of three Montrealers accused of killing four family members is now in the hands of the jury after the trial judge finished giving his instructions on Friday.

The jury is set to begin its deliberations on Saturday at 10 a.m. ET.

Mohammad Shafia, 59, Tooba Yahya, 42, and Hamed Shafia, 21, are each charged with four counts of first-degree murder in the deaths of four family members. They have all pleaded not guilty to the charge.

The three Shafia sisters — Zainab, 19, Sahar, 17, and Geeti Shafia, 13 — and Rona Amir, Mohammad Shafia's first wife in a polygamous marriage, were found drowned in a Nissan submerged in the Kingston Mills lock in eastern Ontario in June 2009.

In his 200-page charge to the jury, Judge Robert Maranger said jurors can deliver a verdict of second-degree murder against some or all of the three accused. The lesser charge doesn't require the same proof of planning and premeditation.

In the case of first-degree, Maranger told jury members in Kingston, Ont., that they must be satisfied beyond a reasonable doubt that the accused killed the four victims and that the killings were planned and deliberate, he said.

"A planned murder is one that is committed as result as of the scheme or plan that has been previously formulated or designed," he said.

For each of the accused, he told the jury, the verdicts available to them are first-degree murder or second-degree murder. He reminded the jury that the accused do not have to prove their account of events. The burden of proof falls on the Crown.

Aiding and abetting

Maranger also instructed the jury on the aspect of aiding and abetting. In Canadian law, a defendant can be found guilty of an offence if the Crown proves, beyond a reasonable doubt, that a person either assisted in the commission of an offence by the principal offender or encouraged a principal offender to commit an offence.

The Crown does not have to prove both, the judge told the jury.

"Please remember the question for you to decide is what the accused actually intended," he said. "If you are left with a reasonable doubt whether the accused had intent to aid or abet, you'd find the accused not guilty."

Earlier, Maranger said prosecution would face a near impossible task to prove with absolute certainty every element of their case.

Their responsibility is to find proof beyond a reasonable doubt, Maranger told the jury.

Maranger asked them to carefully consider the evidence presented before them during the extensive four-month trial and cautioned them that their responsibility is significant. They are expected to begin deliberations today after more than four months of witnesses, arguments and evidence.

Throughout the trial, the defence maintained the deaths were an accident — the result of a joyride with an inexperienced driver at the wheel.

Courtroom full throughout trial

However, the prosecution countered that the deaths were cold and deliberate murder — planned, deliberated, executed and covered up equally by each of the accused.

The motive, the Crown asserted, was the restoration of the family's honour, tainted by the behaviour of the victims and alleged betrayals.

The court has heard testimony from teachers, social workers, technological experts, police, medical professionals, family members and two of the accused themselves in 40 days of court proceedings.

The trial has garnered significant attention as well, drawing media from across Ontario and Quebec and a mass of spectators who would line up early in the morning for a seat in the 150-person courtroom.

On more than one day, people were turned away because the room was at capacity.