A court is hearing that a young man accused of killing his sisters saw them plunge into a canal in a car, but didn't call for help.

Hamed Shafia, 20, and his parents Tooba Mohammad Yahya, 41, and Mohammad Shafia, 58, are each charged with four counts of first-degree murder.

Three teenage Shafia sisters, Zainab, 19, Sahar, 17, and Geeti, 13, along with Mr. Shafia's first wife in a polygamous marriage were found dead inside a car submerged in the Rideau Canal in June 2009.

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The Montreal family told police that Zainab had taken the car keys while they were stopped at a motel in Kingston, Ont., on their way home from a vacation and must have accidentally driven the car into the water.

But a man Mr. Shafia hired as a private investigator is testifying that Hamed told him a different story, that he saw the car go into the water, so he dangled a rope over the ledge to check for signs of life.

He saw none, Hamed told the investigator, so he drove home and didn't tell anyone because he thought he would get in trouble for letting his sister drive without a licence.