The Montreal mother at the centre of the Shafia murder trial on Friday denied that she killed her daughters, telling the Kingston, Ont., court that her family are "not murderers."

Tooba Yahya made the comments in court after prosecutor Gerard Laarhuis laid out in detail how the Crown believes Yahya, along with her husband Mohammad Shafia and 21-year-old son Hamed Shafia, killed her three daughters and her husband's other wife.

The three are charged with four counts of first-degree murder in the June 2009 drowning deaths in the Kingston Mills lock. They have all pleaded not guilty.

"No sir, we are not murderers. We are a very sincere family.… If you were a mother, then you could have known what is a heart of a mother for a child. Don't ever tell me that I killed my children," Yahya said.

Laarhuis alleges the accused drove the victims directly to the locks. He said somebody left the car running, rolled down the window, put the gearshift in neutral and aimed the wheels of the car.

Laarhuis said that next someone reached through the open window and put the car into gear, thinking that on its own power, the vehicle would go into the water.

"What you did not expect, what was not part of the plan, was that the Nissan would get hung up. There was now an emergency, now you had bodies in the car hung up on the edge of the canal," Laarhuis said.

Laarhius said that Shafia or his son got behind the wheel of their Lexus and, as described by a collision expert, hit the Nissan into the canal, damaging both vehicles and causing the Nissan to spin as it sank.

But Yahya denied the account.

The prosecutor has made the suggestion that the three daughters and Amir were dead when their bodies were put in the car then pushed into the water. However, there's been no proof offered to the court of the theory.

A forensic expert who testified said the cause of death was drowning, but he couldn't say whether the four family members drowned in the canal locks or elsewhere.

Yahya has been testifying in the Kingston, Ont., courtroom since Monday about her recollection of the circumstances surrounding the deaths of her daughters Zainab, 19, Sahar, 17, Geeti, 13, and the first wife in her polygamous marriage, Rona Amir.

The accused maintain the deaths were an accident that occurred when inexperienced driver Zainab Shafia took the car without permission and took her sisters and Amir on a joyride.

Earlier Friday, Yahya was questioned by Laarhuis about her brother's claim that her husband told him he was planning to kill their 19-year-old daughter Zainab

Yahya said in court that she didn't know about her brother's claim regarding the threat until the funeral and that her husband and her brother had been "enemies"

Tooba Yahya arrives at court Friday for another day of testimony. (Lorian Bélanger/Radio-Canada)

"How could I have believed [him]?" she said. "How is it possible that I can accept someone who is [an] enemy of 20 years?"

She said if her brother was concerned about the safety of the children, he should have called police and told her about her husband's alleged plan.

Laarhuis asked Yahya if she felt there would have been a risk to her own safety if she called police and left with the children.

"I never expected that from Shafie," she said. "I never expected Shafie to be such a person to kill his children.… If a person knows their children are in danger, a person will do all the things to safeguard the life of their children."

Yahya was not suggesting that Shafia was involved in deaths, only that she never felt unsafe or that Shafia wasn't the type of person who would harm her or the children.

Yahya also testified on Friday that it's common for Afghan men who are angry at their daughters to call them "whores."

Yahya was questioned by Laarhuis about several incidents when her husband was angered by his children. Shafia is heard on wiretaps before their arrests calling the deceased girls treacherous and whores.

Yahya testified that the level of anger heard on those wiretaps was the same kind of anger Shafia expressed during incidents where he believed the girls misbehaved.

"Kids would hear these rants and uncontrollable rage and you're saying that didn't cause you any concern for the safety of your children?" Laarhuis asked.

"These are something that was recorded in our ears for many years. Most Afghan people are the same. When they are angry they are telling and swearing. It's not just Shafia but most Afghan men and women. They are the same," Yahya said.

Laarhuis asked Yahya if she was saying that Afghan men, when they're mad at their daughters, routinely call them whores.

"Sometimes when they get very angry — yes," Yahya said.

The bodies of the four women were found submerged inside the family's Nissan sedan in the Kingston Mills lock. The family, which moved to Canada in 2007, was allegedly en route home to Montreal after a visit to Niagara Falls. The Crown's case alleges a so-called honour killing in which the girls were killed because their behaviour and forbidden boyfriends brought shame to the family

Yahya said she has never heard of an honour killing and called the notion "stupid."

She has spent much of the week trying to explain some evidence presented by the prosecution, including an interrogation taped after her arrest in July 2009 in which she admits to being at the lock that night and fainting after hearing a splash.

In court, Yahya said that was a lie she concocted in response to evidence presented to her by police. She said she was under immense pressure from the interrogator and was under the impression, based on a conversation with another officer, that her son was being tortured.

With files from CBC's Melinda Dalton, Dan Halton and The Canadian Press