KINGSTON, Ontario – A jury on Sunday found an Afghan father, his wife and their son guilty of killing three teenage sisters and a co-wife in what the judge described as “cold-blooded, shameful murders” resulting from a “twisted concept of honor.”

The jury took 15 hours to find Mohammad Shafia, 58; his wife, Tooba Yahya, 42; and their son Hamed, 21, each guilty of four counts of first-degree murder in a case that shocked and riveted Canadians from coast to coast. First-degree murder carries an automatic life sentence with no chance of parole for 25 years.

After the verdict was read, the three defendants again declared their innocence in the killings of sisters Zainab, 19, Sahar, 17, and Geeti, 13, as well as Rona Amir Mohammad, 52, Shafia’s childless first wife in a polygamous marriage.

Their bodies were found June 30, 2009, in a car submerged in a canal in Kingston, Ontario, where the family had stopped for the night on their way home to Montreal from Niagara Falls, Ontario.

Prosecutors said the defendants allegedly killed the three teenage sisters because they dishonored the family by defying its disciplinarian rules on dress, dating, socializing and going online. Shafia’s first and second wife was living with him. The polygamous relationship, if revealed, could have resulted in their deportation.

The prosecution alleged it was a case of premeditated murder, staged to look like an accident after it was carried out. Prosecutors said the defendants drowned their victims elsewhere on the site, placed their bodies in the car and pushed it into the canal.

Defense lawyers said the deaths were accidental. They said the Nissan car accidentally plunged into the canal after the eldest daughter, Zainab, took it for a joy ride with her sisters and her father’s first wife. Hamed said he watched the accident, although he didn’t call police from the scene.

After the jury returned the verdicts, Mohammad Shafia, speaking through a translator, said, “We are not criminal, we are not murderer, we didn’t commit the murder and this is unjust.”

His weeping wife, Tooba, also declared the verdict unjust, saying, “I am not a murderer, and I am a mother, a mother.”

Their son, Hamed, speaking in English said, “I did not drown my sisters anywhere.”

But Judge Robert Maranger was unmoved, saying the evidence clearly supported their conviction for “the planned and deliberate murder of four members of your family.”

“It is difficult to conceive of a more despicable, more heinous crime ... the apparent reason behind these cold-blooded, shameful murders was that the four completely innocent victims offended your completely twisted concept of honor ... that has absolutely no place in any civilized society.”

Hamed’s lawyer, Patrick McCann, said he was disappointed with the verdict, but said his client will appeal, and he believes the other two defendants will as well.

But prosecutor Gerard Laarhuis welcomed the verdict.

“This jury found that four strong, vivacious and freedom-loving women were murdered by their own family in the most troubling of circumstances,” Laarhuis said outside court.