KINGSTON, Ont. - A father accused of murdering his three daughters and first wife to preserve the Muslim family's honour convulsed in quiet sobs Monday as autopsy photographs were shown in court.

It was a rare sign of emotion from Mohammad Shafia, who earlier in the proceeding smiled and chatted amiably with his lawyer.

The Shafia's co-accused wife and mother of the girls, Tooba Mohammad Yahya, was allowed to leave court before the testimony in which a forensic pathologist said the females drowned and showed no signs they had taken or been administered drugs or alcohol.

The three teenage sisters and relative from Montreal were found in a car submerged in a canal in Kingston, Ont., in June 2009.

Before the slides were shown, Crown lawyer Gerard Laarhuis warned they could be distressing.

"These are graphic photographs," Laarhuis said. "People need to be prepared to see them."

Shafia's son, Hamed, who is also accused of first-degree murder in the deaths of his sisters, rubbed his eyes as the slides showing the dead women were put up on large screens in the Ontario Superior courtroom.

During his testimony, Dr. Christopher Milroy said unusually extensive toxicology tests were done on the bodies but turned up nothing untoward.

Searches for substances such as cyanide, cocaine, antifreeze, carbon monoxide, various forms of alcohol and other substances all came back negative, Milroy said.

"There was nothing really that we could have tested for that was not tested for," Milroy told the jury trial presided over by Justice Robert Maranger.

Three of the four victims did show mysterious minor or moderate bruising to the top or side of the heads -- clearly evident in the slides -- but Milroy was unable to say what caused the bleeding.

Nor could he say whether the blows that caused them could have rendered the victims unconscious.

He was adamant they would have woken up when they hit the water had they been simply sleeping.

There were no other major signs of trauma to the bodies.

Milroy testified that all four drowned.

"I found no alternative explanation," he said.

However, he was unable to say whether they had drowned in the canal where they were found floating in the black Nissan Sentra, its ignition in the off position, but its gear shift in "low."

The sisters, Geeti, 13, Sahar, 17, and Zainab, 19, were found in the car on June 30, 2009, along with their father's first wife Rona Amir Mohammad. The Crown has given Mohammad's age as 50, but her passport shows she was 52.

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

Court has previously heard how the teens' father was angry at the their behaviour, and considered them a dishonour to the family.

One of the girls had even tried to kill herself a year before her death after pleas to be rescued from the abusive household, court has heard

The family had been on their way back from a trip to Niagara Falls, Ont., when the drownings occurred.

The accused have cast the drownings as accidental.