A jury in Kingston, Ont., has retired for the night after its first day of deliberations in the case of three Montrealers accused of murdering four family members in June 2009.

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

Deliberations are to resume Sunday at 9 a.m. ET.

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.

The seven women and five men on the jury have been sequestered since Friday night and will remain so until they return a verdict.

In his instructions to the jurors, Judge Robert Maranger said Friday they 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 murder, Maranger told jury members that they must be satisfied beyond a reasonable doubt the accused killed the four victims, and that the killings were planned and deliberate.

Family was on vacation

The family had been on route to Montreal when Amir and the three teens died, returning from a short vacation in Niagara Falls, Ont.

The three accused were arrested 21 days after the submerged vehicle was discovered. They maintained the deaths were an accident — that Zainab, who did not have a driver's licence, took the other victims on a joyride and drove into the locks after the family stopped at a motel for the night in Kingston.

The Crown maintained the entire trip was part of a plot to murder the four for betrayals and treachery that had tainted the family’s honour. The murder plot came about after Zainab ran away to a Montreal women’s shelter in April 2009, the Crown alleged, betraying the family by making their domestic problems public.

Since the start of the trial on Oct. 20, jurors listened to more than 40 days of proceedings that included delays for a health emergency with Mohammad Shafia, a power outage caused by an ice storm and an evacuation due to a security threat at the courthouse.

The jury must consider more than 160 exhibits and testimony from nearly 60 witnesses. However, the defence has argued the prosecution's case has been built on "weak" circumstantial evidence.

The evidence includes computer searches made on the Shafia laptop, most often used by Hamed, for phrases such as “Where to commit a murder” and “Can a prisoner have control over his real estate.”

Prosecutor Laurie Lacelle makes her final summation to the jury. (Mike McLaughlin)

The court also heard wiretap recordings of Mohammad Shafia and his wife Tooba after the deaths in which he complained that their daughters "betrayed us immensely. They violated us immensely."

The Crown alleged a murder plot started taking shape when Hamed travelled to Dubai earlier in the month before the deaths and showed his father photos of the teenage girls, including one of Sahar and her boyfriend. The family maintained the pictures were not found until after the deaths.

The Crown said the girls were seen to have brought shame on the Islamic family by dressing in less modest Western garb and keeping secret boyfriends. However, a half-sibling of Shafia testified that the accused was not religious and grew up in a liberal household in Afghanistan.

The defence argued that without conclusive proof of how the car went into the water, no one would know exactly what happened that night and it may well have been an accident.

Journey from Afghanistan

The Shafias moved to Canada in 2007. They fled their native Afghanistan more than 15 years earlier and had lived in Dubai and Australia before moving the family to Montreal and applied for citizenship.

At the time of their deaths, three of the victims were permanent residents of Canada while Amir had a visitors’ visa.

Rona Amir was Shafia’s first wife. The couple wed in an arranged marriage in Kabul, the Afghan capital, before civil war broke out there. Amir wasn’t able to conceive and encouraged Shafia to take another wife, which he did in 1989, marrying Tooba Yahya in another arranged marriage.

Yahya and Shafia had seven children, which Rona helped to raise.

Before jurors retired to their deliberations, Maranger acknowledged they had challenging work ahead of them.

“You’re engaged in deciding a very important matter,” he said. “Good luck, thank you for listening and thank you for your patience.”