Three teenage girls who drowned in a Kingston, Ont., canal feared their father so much they wanted to leave their family home, and kept secret boyfriends prior to their deaths, Crown prosecutors told a jury Thursday in a groundbreaking murder trial.

Prosecutors laid out their case Thursday morning, arguing that a Montreal husband and wife and their adult son should be found guilty of first-degree murder in the drowning deaths of the couple's three teenage girls and the husband's first wife.

The family members couldn't bear the "treachery" of the three sisters having boyfriends, so they drowned them and the father's first wife, pushing a car into a Kingston canal and staging the scene to look like an implausible accident, the court heard Thursday.

Mohammad Shafia and Tooba Mohammad Yehya were arrested and charged with multiple murders in July 2009, three weeks after the bodies of their daughters – Zainab Shafia, 19, Sahar Shafia, 17, and Geeti Shafia, 13 – were fished out of a sunken car found in a canal lock near Kingston.

The body of Shafia's first wife Rona Mohammed was also in the car.

Shafia's son Hamid Mohammad Shafia was arrested and charged along with his parents.

Crown says teens wanted to leave family home

Prosecutors at the trial painted a portrait of a troubled family in turmoil prior to their daughters' deaths.

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The three victims, seen in this undated family photo, complained of beatings at home, court heard.

Originally from Afghanistan, the family was living in Montreal's St-Leonard borough where the older teenage girls kept secret boyfriends, despite fearing their father would kill them.

The Crown said the teens had complained of being beaten by their father and brother at home, and their school had repeatedly called youth protection. 

The eldest daughter, Zainab Shafia, had run away and both of the other two girls had repeatedly told authorities they were afraid and wanted to leave the family home.

The Crown detailed evidence retrieved from a family laptop that showed someone did a Google search on the terms "where to commit a murder," and "bodies of water."

Mohammad Shafia sobbed as prosecutors broadcast photos of his three daughters in the courtroom — while his wife Tooba Mohammad Yehya kept her eyes downcast.

All three accused have pleaded not guilty to the murder charges.

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People lined up early Thursday for a seat in the Kingston courtroom. (Justin Hayward/CBC)

The trial will be the largest ever held in Kingston, and is considered groundbreaking because of its complexity.

Mohammad Shafia and Tooba Mohammad Yehya only speak Dari, so the trial will proceed in English and French with Dari translation, a first in Canada.

During that time, Crown prosecutors will present forensic evidence and could call more than 50 witnesses, including relatives from Europe to argue their case.

The trial is expected to last three months.

With files from The Canadian Press