Three Montrealers accused of drowning four Shafia family members in Kingston, Ont., viewed the deceased as the "diseased limb on the family tree" that needed to be removed, a Crown attorney told jury members on Thursday.

In her closing remarks, Laurie Lacelle said Mohammad Shafia, 59, his wife, Tooba Yahya, 42, and their son Hamed Shafia, 21, were involved in the planning, execution and coverup of their murders.

"Their solution" Lacelle said of the accused,"was to remove the diseased limb entirely and prune the tree back to the good wood."

Lacelle went through the time before the deaths of the three Shafia sisters — Zainab, 19, Sahar, 17, and Geeti Shafia, 13 —and Rona Amir, Mohammad Shafia's first wife in a polygamous marriage. They were found drowned in a submerged Nissan in the Kingston Mills lock in eastern Ontario in June 2009.

Lacelle talked about the warnings that were allegedly given to Yahya from two family members about her husband's intention to kill Zainab. She did nothing, Lacelle said, because she already knew about the plan and was involved in it.

She also told the jury the Nissan was specifically purchased for the murder plot and bought a day before the trip.

Lacelle said that Mohammad Shafia's response that the car was purchased so Zainab would have a car to drive wasn't plausible because there were already plans for Zainab to marry another man so she would soon be out of the house.

"The purchase of the Nissan was part of the murder plan," Lacelle told the jury. "If the plan was to stage an accident that accounted for the deaths of four people, a car would have to be sacrificed, too."

Pieces of the family's Lexus SUV were found at the scene where the Nissan sedan plunged into the Rideau Canal on June 30, 2009.

Yahya's role

Lacelle spent a significant amount of time on Yahya's role in the alleged murder plot.

According to the Crown's theory, Yahya drove the women to the locks in the Nissan and waited there with them until Hamed and Mohammad Shafia returned from dropping the other children at a motel.

Yahya "stayed with them. Stayed at the scene. Kept them unsuspecting," Lacelle said during her closing statement.

"It is inconceivable that Tooba was at the scene — from the time they were alive waiting with her to the time the bodies were submerged in the canal — and wasn't a participant in the murder plan. If she hadn't agreed to participate in the plan or the cover up, then it couldn't have taken place," Lacelle said.

"That means she played a significant role in the murders."

Timeline issues

Lacelle also addressed the timeline issue that defence lawyers said proved the accused did not have enough time to commit the murders.

She said the accused had ample time — around an hour and 15 minutes, possibly longer — to drown the four women, put them in the car and push it into the water.

The defence's argument was largely based on data from traffic cameras in Montreal, which they said showed Hamed in the family's Lexus early on the morning of June 30.

Lacelle pointed out that the traffic camera only caught an image of a silver SUV, not a licence plate or anything that would identify it as belonging to Shafia.

"The highway footage is nothing more than a red herring," Lacelle said. "Don't be distracted by it."

She said Hamed could have left Kingston as late as 3:48 a.m. and still had time to get to Montreal by 6:48 a.m., when cellphone records indicated he received a call from his father, who was at the Kingston motel.

In her summation, Lacelle also reminded jury members that they don't have to know what happened or how it happened precisely to convict the three accused of first-degree murder.

"It should come as no surprise in a quadruple murder where the only witnesses are either dead or on trial, that there may be some holes," Lacelle said, calling the evidence "overwhelming and irrefutable."

"The Crown has proved all essential elements of the offence. You know this is not an accident. It was murder."

The trial was delayed Thursday because of a security issue. Security measures were beefed up, which include the use of metal detectors, for the duration of the trial, officials said.

On Friday, the judge will start his charge to the jury members, who will then begin their deliberations.