KINGSTON, Ont. - Closing arguments in the Shafia family murder trial have resumed after a bomb threat forced an evacuation at the courthouse this morning.

Crown attorney Laurie Lacelle is telling the jury that each of the three accused was responsible for planning and carrying out four murders, executed to get rid of family members causing them dishonour.

Mohammad Shafia, 58, his wife Tooba Yahya, 42, and their son Hamed, 21, have each pleaded not guilty to four counts of first-degree murder.

They're accused of killing teenage Shafia daughters Zainab, 19, Sahar, 17, and Geeti, 13, as well as Shafia's first wife in his polygamous marriage.

The trial resumed under heightened security following the bomb threat.

Justice Robert Maranger made the jury laugh when he said "Well, expect the unexpected," as they filed back in.

Maranger said heightened security measures taken after the threat had slowed down the process of getting the many spectators back inside the building in Kingston.

But he assured the jury the Crown will finish its closing arguments today and, after an early start Friday, he will take the whole day to give his final instructions to the jury. The verdict will be in the jury's hands Friday afternoon or early evening.

In her closing arguments, Lacelle said the three accused "decided that there was a diseased limb on their family tree."

"Their decision was to trim the diseased limb and prune the tree back to the good wood," she said.

The bodies of the four were found June 30, 2009, in a car at the bottom of a canal in Kingston, where the Montreal family had stopped on their way back from a trip to Niagara Falls, Ont.

The Crown alleges it was a premeditated murder, staged to look like an accident after it was carried out. But Patrick McCann, the lawyer for Hamed, told the jury Wednesday that the evidence does indeed fit with the deaths being an accident.

Four months after the family's arrests Hamed told a university student hired on the sly by his father as a private investigator that he was present when the car went in the canal and had witnessed the tragic accident. He didn't call police at the time, and for that he is "guilty of being stupid" and "morally blameworthy," but not of murder, McCann said.

The Crown suggested Wednesday that story was a "complete fabrication" concocted by Hamed to explain the evidence.

While police would only say there was a "security concern," a source told The Canadian Press the reason for the evacuation was a bomb threat.

"I can neither confirm nor deny in regards to specifically a bomb, but we are just stating at this point in time it is a security concern," Const. Steve Koopman said. "As you can see we're taking it extremely seriously."

Koopman couldn't say if the security threat was related to the Shafia trial.

"I cannot say 100 per cent, I think it's relatively coincidental that today that Superior Court Justice Maranger was going to charge the jury and this is the most high profile case in town," he said.

When the proceedings finally resumed, four police officers were posted in the courtroom.

Police said they were notified of the security threat at 9:35 a.m., prior to the start of the day's proceedings in the Shafia case. The building was completely evacuated shortly after police received the call and the three accused were taken offsite.