Legal experts are calling on Calgary police to hand over the investigation of the city's worst mass killing to another agency in order to remove any perception of bias related to the accused, the son of a senior officer with the force.

The Calgary Police Service rejected the notion, saying it has unmatched experience, investigative skills and resources and has already shown how vigorously it is pursuing the case by the speed in which it laid five first-degree murder charges.

Police charged Matthew de Grood, 22, on Tuesday, about 20 hours after he allegedly killed four men and one woman at a house party. Mr. de Grood, 22, is the son of Inspector Doug de Grood, a 33-year veteran of the CPS.

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This, experts say, could create the perception of a conflict of interest. The RCMP, for example, could be brought in.

Calgary police collected evidence at the scene, a rented split-level home near the University of Calgary, and interviewed witnesses on Wednesday.

"Here we have the closest possible family connection you could make – the father of the accused in Calgary's worst alleged mass murder is a senior police officer," said Ian Savage, president of the Criminal Defence Lawyers Association. "Given the high profile nature of this matter, it would complete not just the actual but the appearance of fairness to have the investigation be continued by another agency."

Mr. Savage said there is "no way" the accused murderer's father would influence the investigation, and he does not believe that the CPS would be biased. However, the case should still be turned over to an agency such as the RCMP or the Edmonton Police Service, he said.

"It is interest of all parts of the justice system – the defence of this accused person, the prosecution of this accused person. It is imperative that fairness and lack of any bias be eliminated from a major criminal investigation like this," he said. "The public is entitled to what we call the appearance of fairness. Not just in actuality, but the appearance as well.

"So to avoid any suspicion by anyone inside the system or outside the system, it is best an independent, separate, agency continue the investigation," Mr. Savage said.

Calgary police spokesman Kevin Brookwell said the Crown is providing the necessary oversight, and the force is pursuing the case as it would any other, despite the family connection.

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Alberta's Justice Department has appointed Crown prosecutors from Edmonton to the case, becasue of the relationship to a senior officer.

Mr. Brookwell said Mr. de Grood's father remains on the job, as the accused, who is in custody at a forensic psychiatric centre, awaits his first court appearance on Tuesday.

"We have to be clear, too – this is not a police officer we're investigating. [In] every investigation,we're not going to be checking in to see what connections there are to members of our service," he said. "We have to go into an investigation like this, particularly an investigation of this magnitude, with the full knowledge that we're going to do what we need to do to ensure that the case that we put through the courts is above reproach."

The Calgary Police Commission, which provides civilian oversight to the CPS, was not available to comment on the issue.

Irvin Waller, a professor in the criminology department at the University of Ottawa and president of the International Organization for Victim Assistance, is among those who believe it is troublesome to have the CPS continue the investigative work.

"The police investigation into any crime, particularly with five people killed, needs to be independent and seen to be independent," he said in an e-mail. "The Calgary Police Service is one of the best in the world, but investigating an accused who is the son of long-time serving officer is unnecessarily testing their limits."

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He, too, suggested police from Edmonton or the Mounties could step in.

All of victims were in their 20s. They were at a house party near the University of Calgary, celebrating the end of the school year. There were about 30 people at the party at its peak, and about 20 when the victims were attacked with a large kitchen knife, police said.

Mr. Brookwell said the accused mingled for an undetermined period before the attacks began. Police have seized electronic devices and other items in their investigation.

Two of the victims were living at the rented house, he said.

Chris Sherrin, an associate law professor at the University of Western Ontario, agrees it would be wise for the local police to bring in outsiders. "I think it would probably be a good idea – if only, at the very least, to maintain the perception of impartiality," he said.

Allan Fay, Mr. de Grood's defence lawyer, said it is difficult for him to comment on such matters.

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"Obviously I have a concern that certain people might conclude that he is being given a special break because he is a police officer's son, or the contrary – that he's being dealt with more harshly because the Calgary Police Service doesn't want to look like it's acting in a biased fashion," he said.

"I certainly think for the optics that it wouldn't hurt for an outside agency to carry on the investigation, but the fact is that the Calgary police have and continue to carry out this investigation."