A Montreal couple and their son were convicted Sunday of murdering four female relatives in what the judge described as a "cold-blooded" and "heinous" crime.

Mohammad Shafia, 58, his wife Tooba Yahya, 42, and their son Hamed, 21, were each found guilty of four counts of first-degree murder in the deaths of Shafia's three teenaged daughters and his first wife.

Sisters Zainab, 19, Sahar, 17, and Geeti, 13, along with Shafia's other wife Rona Amir Mohammad, 52, were found dead on June 30, 2009 in a car at the bottom of a canal in Kingston.

From the start of the trial in October, prosecutors argued these were "honour killings" -- the Afghan-Canadian family's answer to the young sisters' perceived shameful behaviour.

"It is difficult to conceive of a more despicable, more heinous, more honourless crime," Justice Robert Maranger said in court after the verdict was delivered Sunday.

"The apparent reason behind these cold-blooded, shameful murders was that the four completely innocent victims offended your completely twisted concept of honour...that has absolutely no place in any civilized society."

Jurors reached the guilty verdict after a 10-week trial, 58 witnesses and 15 hours of deliberations. One juror burst into tears as the verdict was read, reported CTV News' Montreal Bureau Chief Genevieve Beauchemin.

A first-degree murder conviction carries an automatic life sentence with no chance of parole for 25 years.

One-by-one, Mohammad, Tooba and Hamed maintained their innocence when asked by the judge if they wanted to say anything.

"We are not criminal, we are not murderer, we didn't commit the murder and this is unjust," Mohammad Shafia told the court through a translator.

"Your honourable justice, this is not just," Yahya said, also through an interpreter. "I am not a murderer, and I am a mother -- a mother!"

Hamed addressed the judge in English, saying: "Sir, I did not drown my sisters anywhere."

Beauchemin noted that Hamed appeared to be the most emotional of the three, slumping in his seat as the verdicts were read.

At one point his parents rubbed his back, presumably in a bid to console him.

Trial ‘gave victims a voice'

As the trio was led out of the courthouse in front of a throng of journalists and flashing cameras, Mohammad Shafia loudly said: "Wrong."

Outside the Kingston courtroom, prosecutor Gerard Laarhuis said it was a good day for Canadian justice but also a sad day given it involves the death of four women.

"This jury found that four strong, viviacious and freedom-loving women were murdered by their own family in the most troubling of circumstances," he said.

Some onlookers in a crowd on the court steps cheered when Laarhuis spoke while others heckled the prosecutor.

"This verdict sends a very clear message about our Canadian values and the core principles of a free and democratic society that all Canadians enjoy and even visitors to Canada enjoy," Laarhuis said.

Staff Sgt. Chris Scott, who led the Shafia investigation, thanked prosecutors for their work.

"I would just like to add one thing, assistant Crown attorney Gerard Laarhuis and (prosecutor) Laurie Lacelle did an exceptional job," he said amid cheers.

"Their passion, their work ethic, gave these victims a voice when they had none and I appreciate their work," he said.

In a statement following the verdict, Justice Minister Rob Nicholson called honour killings "barbaric and unacceptable in Canada."

"This government is committed to protecting women and other vulnerable persons from all forms of violence and to hold perpetrators accountable for their acts," he said.

Outside court, Shafia's lawyer Peter Kemp said he believes the jury was swayed by wiretap conversations in which his client called his dead daughters whores.

"He wasn't convicted for what he did," Kemp said. "He was convicted for what he said."

Hamed's lawyer, Patrick McCann, said his client will appeal. He believes Hamed's parents will do the same.

Legal analyst Steven Skurka told CTV News this is a precedent-setting case in Canada, where honour killings are "a rare phenomenon."

"It really is quite an unusual and an astounding case," he said. "In order to restore family honour, family reputation, in order to cleanse the family's shame...(these women) needed to be killed."

Prosecutors had argued that the young Shafia sisters had shamed the conservative Afghan family -- and especially its patriarch -- by wearing revealing clothing, refusing to don hijabs and having boyfriends.

The jury heard that Zainab had previously run away from home and was briefly married to a Pakistani man Shafia did not approve of. The marriage was annulled within 24 hours.

Sahar also had a forbidden boyfriend, while the youngest of the three, Geeti, told her teachers she wanted to be placed in foster care. Mohammad Shafia's first, infertile, wife had protected the girls, especially Sahar, whom she had been raising as her own, court heard.

Shafia and Yahya had seven children in total. After their arrests, the remaining children, all minors, were placed in foster care.

Court also heard damning wiretapped conversations between the accused in which, at one point, Shafia said of his dead daughters: "God's curse on them … May the devil shit on their graves."

Teachers, child protection workers and police officers testified about reports from the girls that they were afraid of their father and brother and wanted to run away from home.

The Crown painted a picture of a highly dysfunctional polygamous family, with Shafia and Hamed exerting control over female members of the household and the two wives fighting for Shafia's affections.

Yahya and Shafia refuted the Crown's theory and evidence, saying they loved their children and would have never killed them. In interviews with police and on the stand, the couple maintained the deaths were a tragic accident.

The night the sisters and Mohammad disappeared, Zainab had asked to borrow the car keys, her parents told police. Zainab, an unlicensed and inexperienced driver, must have taken the group on a joyride and somehow ended up in the canal, they said.

But court heard conflicting versions of what happened that night. Yahya had initially told police the two Shafia men were at the canal when the car went in the water. But during her testimony, she told court that was lie.

Hamed never took the stand in his own defence, but court heard a taped conversation in which he admitted to a private investigator that he was at the scene.

Hamed said he had followed his sisters in a separate car out of concern and rear-ended them at the canal. While he was picking up pieces of shattered headlight, he heard a splash and ran over to the edge of the water. He said he dangled a rope and called his sisters' names, but hearing no response, drove off and headed home to Montreal without calling 911.

While his client was "stupid" to make such a "terrible" mistake, he was no murderer, Hamed's lawyer told the jury.

During closing arguments, defence lawyers for all three accused bristled at the suggestion of honour killings, saying the Shafia daughters were prone to lying and exaggerating their problems at home.

The defence also said the Crown failed to prove that any murder had been committed, failing to explain where and how the Shafia sisters and Mohammad were killed.

A pathologist testified that the cause of death for all four was drowning, though he couldn't conclude if they drowned in the canal. The Crown alleged the four were dead before their car hit the water.

The court also heard from police and technical witnesses who testified it was unlikely the car could have fallen into the canal by accident.

With files from The Canadian Press