A Montreal woman accused of killing her three daughters and her husband's first wife told police in a videotaped interrogation that she was not aware the father of her children was going to kill their girls.

The police videotape was shown to a jury in Kingston, Ont., Wednesday, during the canal lock death trial where the woman, her husband and her son face multiple first-degree murder charges.

Tooba Mohammad Yahya, 41, Mohammad Shafia, 58, and Hamed Mohammad Shafia, 20, have each pleaded not guilty to four counts of first-degree murder.

They are accused of killing the family's three teenage girls and the father's first wife.

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The family is alleged to have used their Lexus SUV to push this Nissan Sentra into the canal in the middle of the night. (Trial evidence photo)

The three teenage Shafia sisters, Zainab, 19, Sahar, 17, and Geeti, 13, along with Shafia's other wife, Rona Amir Mohammad, 50, were found dead inside a submerged car in June 2009 in the Rideau Canal.

The interrogation shows Yahya crying and appearing worn out, as a police officer asks her questions about the night in June 2009 when the four were found dead.

'This is not an accident, madam'

For much of the interview, RCMP Insp. Shahin Mehdizadeh, who was brought in to conduct the interview in Farsi, goes over Yahya's story with her piece by piece, pointing out evidence that contradicted her account and accusing her of lying to him.

"This is not an accident, madam," he says. "You know what has happened here … I don't want the lies. I don't want the lie that Zainab came and took the key and after that I didn't see her.

"Someone became God that night and decided that these three girls and this lady should have been killed," Mehdizadeh says.

"When they did this, they didn't do their work right, I am telling you."

Eventually, Yahya starts changing her story, bit by bit, but begins by asking that Mehdizadeh not tell her husband.

Girls never at hotel

She admits she was with her son and husband at the canal that night, and that the four dead people never made it to the hotel.

Yahya tries to pin it on her husband, saying she and Hamed were walking by the canal and they heard a splash, ran over and saw the car in the water. It was at that point that she fainted, she said.

Mehdizadeh questioned why if that is in fact what happened, no one called police.

With files from The Canadian Press