A surviving child of a Montreal couple accused of killing four family members has lied to and manipulated authority figures in the past and may not be telling the truth in court, a prosecutor suggests.

The son of the couple who are accused, along with their oldest son, of committing so-called honour killings, is testifying for the defence at the Shafia family murder trial and was subjected to a lengthy and testy cross-examination Tuesday that culminated in his sudden request to use the washroom.

On Monday, the son testified he might have been responsible for one of the more apparently damning pieces of evidence against his family members. On June 20, 2009, just 10 days before the drowning deaths of his sisters and father's first wife, someone used the family computer to search "where to commit a murder."

The son, who can't be identified due to a court order, said he was suicidal at the time and though he doesn't remember entering that specific search, it might have been him because he didn't know the word for suicide.

He said he was suicidal because his eldest sister, Zainab, had run away to a shelter. But that was on April 17, 2009, and she returned home two weeks later, court has heard.

The computer search came on June 20, three days before the family left on a trip to Niagara Falls, Ont., that would end in the deaths on June 30. At that time, the witness testified he was happy and so was everyone else in the family. Life was good, he said.

Confusion about dates

The son appeared to get confused about the dates Tuesday and in an exchange of escalating tension with Crown attorney Gerard Laarhuis, the son abruptly turned to the judge.

"Your honour, may I be excused to go to the washroom, please?" he said.

The court took a break and when Laarhuis returned to the topic later in the afternoon he started questioning the witness about how he could not know the word for suicide. The son suggested the search was a result of Google's auto-complete function, but Laarhuis noted those precise words were typed.

"It was after April 17th, right?" the son asked.

"No, you're wrong," Laarhuis replied. "It was during your happy period, the 20th [of June]. Do you want to change your testimony about that now?"

"No, not at all," the son said.

The witness has admitted manipulating teachers in the past by telling them lies and has admitted manipulating police in the past by telling them lies, Laarhuis said.

"So where do you draw the line on manipulating people and telling lies?" he asked. The son responded, "When it goes too far, I guess."

His parents Mohammad Shafia, 58, and Tooba Yahya, 42, and his brother Hamed, 20, have each pleaded not guilty to four counts of first-degree murder.

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Mohammad Shafia leaves a holding cell at the Frontenac County Courthouse in Kingston, Ont., on Dec. 8. Shafia, his wife and son, Hamed, have each pleaded not guilty to four counts of first-degree murder. (Lars Hagberg/Canadian Press)

The Crown alleges they killed three Shafia sisters and Shafia's first wife in a polygamous marriage over family honour.

The bodies of Zainab,19, Sahar, 17, Geeti, 13, and Rona Amir Mohammad, 52, were found in a car submerged in a canal in Kingston, Ont., on June 30, 2009.

Shafia, Yahya and Hamed have told police that the night of the deaths Zainab came into their motel room to borrow the car keys. The Crown alleges the now-deceased children were killed before the family checked into the motel, and that they made up the story about the car keys to place the girls at the motel alive, which would fit with their assertion that the deaths were a joyride gone wrong.

The son, and brother to the girls, was hammered by Laarhuis at another point about his statement to police that Zainab came to the motel room that night to borrow his cellphone.

Laarhuis suggested that never happened, and further, that inconsistent statements to police that it might have been his mother who wanted to borrow his phone point to a mistake on his part.

"I'm putting to you, that's where you're getting confused, because the story was supposed to be Zainab came and asked for keys, but you got confused," Laarhuis said. "You got mixed up and you said she came and asked for a cellphone."

The brother denied the suggestion.

He also denied that one of his roles in the family was to report back to his parents and Hamed on the behaviour of Sahar and Geeti at school.

But many of his answers during his cross-examination were unclear, which sometimes elicited chuckles from members of the public watching the trial.

At one point, he said he went to visit the site of the deaths once afterward, to see where his sisters had died. Laarhuis suggested he visited a second time, and the brother responded: "Uh, yes. I'm not sure. I don't recall. I don't remember it."

"You said yes ... What's that about?" Laarhuis asked.

"Maybe I was back there in Kingston, but not on the [specific] site," the brother said.

Laarhuis also suggested the family had stopped at the site of the deaths to use the washroom at the beginning of their trip, which the father had testified to last week, but the brother said he wasn't sure. He said he remembers stopping in a park, but wasn't clear if there was water at that park, saying, "Uh, yes. I don't know. I'm not sure."

He also denied several incidents involving his family that the court has heard other witnesses testify to, including his own father.