The Independent Investigation Unit of Manitoba is well aware of the public appetite for information about Friday's police shooting of Mark Dicesare in Winnipeg, but people shouldn't expect quick answers, the organization's director says.

"This is an extraordinarily large investigation, both in terms of the scope, its physical size — the area of the city that's part of the matter — as well as the number of witnesses we have to interview," said IIU executive director Zane Tessler, a former Crown attorney.

The car driven by Mark Dicesare, along with a police cruiser, were left damaged following a police chase that ended with Dicesare being shot. (CBC) "There is a fine balance between the desire for expediency and the expectation for thoroughness. We want to make sure our work is done as thorough, as complete and as professionally as possible. This is a very involved, very detailed, very extensive investigation."

Dicesare, 24, was shot dead by police at the edge of the city's Tuxedo neighbourhood after a 45-minute chase.

A police officer saw him driving erratically in the Charleswood neighbourhood and began following him.

It is alleged that at some point Dicesare was seen holding a gun, prompting dozens of cruisers to become involved in the pursuit that went through the Tuxedo and River Heights neighbourhoods as well.

It ended with his car surrounded by cruisers in a field at the corner of Grant Avenue and Kenaston Boulevard, where officers opened fire just after 1 p.m. CT.

Of the 25 officers who responded to the scene, five were directly involved in the lethal shooting, a police spokesman has said. All five are off duty while their health and well-being is assessed.

Mark Dicesare died after he was shot by police on Friday. (Instagram) The investigation into the incident was immediately taken over by the IIU, which examines all serious incidents involving police officers in Manitoba.

IIU members quickly responded to the scene and began measuring and photographing as well as gathering and cataloguing evidence.

Tessler said investigators were there from Friday afternoon and well into the evening, then back all day and evening Saturday and again all day Sunday.

He would not provide a timeline for how long he thinks the investigation will take, saying it's the largest one his office has undertaken. Nine investigators — the entire IIU team — are working on it.

There are dozens of witnesses to interview, cellphone videos to review, as well as forensics and firearms experts to consult with over the next several weeks.

"It's a very daunting process but one that we are ready for," Tessler said, adding an autopsy is currently being conducted on Dicesare and no results are available yet, so he would not comment on whether drugs or alcohol played a part in Dicesare's actions.

Tessler would also not comment on whether Dicesare did, in fact, have a weapon. The IIU does not have that information "at the ready yet," he said.

Anyone else with information about the incident is asked to contact the IIU, said Tessler, adding he would make a formal public plea Monday afternoon.

Psychologists treat five officers directly involved

The five officers who were directly involved in the shooting are being treated by psychologists, said George Van Mackelbergh, Winnipeg Police Association vice-president.

Eventually those officers will be interviewed by the IIU.

IIU executive director Zane Tessler says there is a fine balance between the desire for expediency and the expectation for thoroughness, so the public shouldn't expect 'instantaneous information' from the investigation into the death of Mark Dicesare. (CBC) Van Mackelbergh said while officer-involved shootings are not common, police know they do happen.

"Anybody that gets into this profession would be foolish not to know that this is a possibility," he said.

"You pray it never happens.… When it does, you will act in a manner in which you're trained, but you still have to process it afterwards."

He called Winnipeg a busy police jurisdiction and even a violent one, but in spite of that, there are few that end in lethal shootings.

"Unfortunately it's a very violent jurisdiction. But what I'm very proud of is that, if you look at the number of violent calls that our members attend to and how very, very, very few of them end up this way, that's very remarkable," he said.

'Police officers not required to wait for gun to be pointed at them': Use of force expert

Use of force expert Joel Johnson told CBC police do not have to wait for the gun to be pointed before taking preemptive measures.

"When this subject emerged from his vehicle, having already demonstrated deadly force behaviour, and made a deliberate move to access something in his pocket … police officers must consider the appropriate contextual cues and the possibility that the subject is accessing [or] has accessed a weapon," he said.

While Johnson did not witness the incident, he said it appears Dicesare demonstrated "an ability and willingness to engage in deadly force behavior."