The father accused in the Kingston, Ont., canal deaths told police in an interrogation video shown during his trial Thursday that he wondered if someone drugged or choked his daughters prior to their deaths.

Mohammad Shafia was interrogated a day after the bodies of his three daughters were found in June 2009.

Shafia told police in the video that his eldest daughter, Zainab, 19, took the car keys and went on a joyride and had a terrible accident. Weeks before he was arrested, Shafia was recorded telling police he didn't know how their car got in the water at the Kingston Mill Locks.

"If someone drugged them or choked them, I want to know," Shafia told police.

"Up until the point the police told me, I wouldn't have even imagined this. I would have thought they went to Montreal," Shafia said.

Shafia, 58, his wife, Tooba Mohammad Yahya, 41, and their son, Hamed Mohammad Shafia, 20, have all pleaded not guilty to four counts of first-degree murder in the deaths of Zainab, 19, Sahar, 17, and Geeti Shafia, 13, as well as Rona Amir Mohammad, 50.

The prosecution already told the court the autopsies revealed no signs of drugs in the victims' bodies. The autopsies were delayed by a day because of the July 1 holiday.

Court hears from victims' teachers

Also on Thursday, the trial heard testimony from teachers at the Montreal high school attended by two of the victims.

Antonella Enea testified she taught Sahar for two years before the teen's death. Enea said Sahar confided in her, and the teacher told the court she twice called youth protection services.

Enea said the last call was made in June 2009 after Sahar said she was afraid because her father was returning from overseas, and one of her siblings was going to tell him she was "a whore."

The teacher testified she called youth protection officials and they advised her to locate a shelter in the community where Sahar could go if she needed to leave her home.

Youth protection services told Enea there was no social worker assigned to Sahar's case, even though a complaint was made a year before.

On Wednesday, two school vice-principals told the jury they were concerned about the Shafia girls after a series of unexplained absences and behaviour that was growing increasingly out of character for them.