Police are facing growing criticism over their handling of the Bourke St massacre including whether they let alleged driver Jimmy Gargasoulas escape before the carnage began.

Officers had been trying to arrest Gargasoulas, 26, for as long as 16 hours before he is alleged to have mowed down pedestrians in the CBD, killing five people - including two children - and injuring dozens more.

Victoria Police Commissioner Graham Ashton has confirmed police did try and "box in" the Holden Commodore on more than one occasion.

"On this last occasion we were trying to get him from the early morning ... We did get close to him a couple of times," Ashton told Neil Mitchell on3AW.

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"Indeed we were trying to pursue him on one occasion trying to pick him up."

He said there were also times pursuing police tried to "box in" the car, including in the CBD on Swanston St.

Matthew Si - one of those killed in the Melbourne rampage. Photo / Supplied
Matthew Si - one of those killed in the Melbourne rampage. Photo / Supplied

Another time was on the Bolte Bridge when Gargasoulas' girlfriend Akiir Muo managed to get out of the car. Witnesses say the car was "surrounded" by police at the time, something not denied by Ashton - but he still managed to get free and head towards the CBD.

Social media has been flooded with angry members of the public who want to know why he was not stopped. Footage of Gargasoulas doing burnouts outside Flinders Street Station have also infuriated Australians, who believe there was enough time to do something to stop him before he entered Bourke St Mall.

These are the key questions police are facing as the Coroner begins her "forensic" examination about what could have been done differently.

WHY DIDN'T THEY RAM THE CAR?

Dimitrious 'Jimmy' Gargasoulas. Photo / Facebook
Dimitrious 'Jimmy' Gargasoulas. Photo / Facebook

Ashton told 3AW it wasn't police policy to ram vehicles as a means of stopping them, largely due to the danger it puts police staff in.

"To ram cars isn't police policy, it isn't the normal thing to do," he said.

Blocking a car in was another strategy that was used and police did attempt this. Ashton said the option of ramming a car was something that would only occur in "exceptional" circumstances.

"But that would have been going through those officers' minds that morning."

He wasn't aware of a request by staff, unrelated to the Bourke St incident, for special cars that were able to ram vehicles.

WERE THE POLICE CALLED OFF?

Photo / News Limited
Photo / News Limited

Within hours of the tragedy sources within the police said there had been seven occasions where they could have safely tried to intercept Gargasoulas.

But the allegation is that on each occasion staff were told not to attempt it by their superiors.

Police Association secretary Detective Senior Sergeant Ron Iddles told Fairfax one of those times was late morning on Chapel St while the Commodore was in heavy traffic.

"It couldn't move. That's the appropriate time to take a car out," he said.

During his 3AW interview, and also during a media conference at the weekend with Premier Daniel Andrews, Ashton said he didn't believe there had been seven opportunities.

"That's not what I'm seeing on the [police] logs."

However, he did not deny there had been opportunities.

"As I've said before, there's opportunities where you look for opportunities and look for the safest course of action ..."

WHY DIDN'T POLICE ACT OUTSIDE FLINDERS STREET STATION?

'Jimmy' Gargasoulas outside Flinders Street Station. Photo / News Limited
'Jimmy' Gargasoulas outside Flinders Street Station. Photo / News Limited

Ashton said there were police there, including uniformed staff who were carrying out anti-social campaigns.

When the burnouts began their immediate focus was to stop other cars entering the intersection, Ashton said.

But other police units, both in the air and on the ground, that had been tracking Gargasoulas were closing in.

"At that stage we had the air wing over this person and cars trying to close in on him at the time."

THE CORONER WILL DECIDE

Jess Mudie, 22, who died in Burke St. Photo / Instagram
Jess Mudie, 22, who died in Burke St. Photo / Instagram

Ashton said he was confident the police hadn't failed and was backing his staff "100 per cent".

Ultimately, it will be up to the coroner to decide if the operation contained serious flaws because it would be examined in "forensic" detail.

"Everything I'm seeing is pointing to police members making split decisions on the run, life and death decisions, about trying to apprehend an offender ... They're feeling it [now] thinking 'Gee did I make the right decision'," Ashton said.