Someone used a Montreal family's home computer to search the internet for information about murder just days before three sisters and their father's first wife were found dead in a car submerged in a canal near Kingston, Ont.

Tooba Mohammad Yahya, 41, her husband, Mohammad Shafia, 58, and their son, Hamed Mohammad Shafia, 20, have each pleaded not guilty to four counts of first-degree murder, in connection to the deaths of the family's three eldest daughters and the elder Shafia's first wife. They're on trial in Kingston.

The victims are three of Shafia's daughters: Zainab, 19, Sahar, 17, and Geeti, 13, as well as Rona Amir Mohammad, 50, Shafia's first wife, who lived with the family in a polygamous relationship.

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The victims. (Radio-Canada)

The family was on the way back from a trip to Niagara Falls, Ont., when the bodies and sunken car were discovered at the bottom of a Rideau Canal lock in Kingston, Ont.

A Kingston police officer testified Thursday about searches conducted on a laptop used by Hamed Shafia such as "documentaries on murders," "can a prisoner have control over their real estate," "where to commit a murder" and numerous searches for areas with bodies of water.

The trial jury spent part of Thursday morning at the Rideau Canal lock, where the victims' bodies were retrieved in June 2009.

Crown prosecutors requested the visit to show jury members the crime scene. Mohammad Shafia and Hamed Mohammad Shafia joined the jury on the canal visit, under close police watch. Authorities blocked off nearby streets to control access to the site.

The court granted Tooba Mohammad Yahya's request to skip the visit.

On Wednesday, the jury heard testimony from a police investigator who said collision evidence from the crime scene suggests the Nissan Sentra carrying the victims was pushed into the canal.

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A collision expert testified about damage found on two cars. (Radio-Canada)

OPP officer Chris Prent testified that there was no way the car could have accidentally fallen into the canal lock.

"Another vehicle was used to push the Nissan Sentra into the canal. Damages on both vehicles coincide," Prent said. The Nissan's driver seat was leaning too far forward to be able to operate the car, and the airbags never inflated.

On Tuesday, the jury watched an underwater video shot by Glenn Newell, an OPP diver assigned to examine the submerged car.

The video shows eerie images of the victims' bodies floating freely inside the car, which was stuck in first gear. None of the victims were wearing seat belts.

The defence is expected to argue that the four women died as the result of a road accident.

The Crown alleges the girls' family thought the teens were dishonoring them by having boyfriends, so they killed them and staged the scene to look like an accident.

The defendants have pleaded not guilty. The trial is expected to last into 2012.