Nova Scotia RCMP say the fact the gunman who went on a deadly shooting rampage last weekend looked like a police officer made trying to catch him dangerous and complicated.

"I can't imagine any more horrific set of circumstances when you're trying to search for someone that looks like you," Supt. Darren Campbell said during a news conference on Friday.

"That obviously was an advantage that the suspect had on police, that he had on the public."

Police encountered the gunman about 13 hours after the first 911 call came in on Saturday night. He was shot and killed at a gas station in Enfield at 11:26 a.m. local time on Sunday — about 90 kilometres from where the first victims were found.

Twenty-two people were killed, including an RCMP officer, a family of three, health-care workers, an elementary school teacher and two Correctional Service Canada employees.

Police said there were three clusters of shooting events Saturday night and into Sunday: the first in the Portapique area, the second about 40 kilometres north in Wentworth and Debert, and the third farther south in Shubenacadie and Enfield, which is about 100 kilometres from Wentworth.

WATCH | RCMP provide detailed timeline of N.S. mass shooting:

In his opening statement on Friday, Supt. Darren Campbell described how RCMP began to respond to three "clusters" of incidents in Nova Scotia. 2:37

Police first spoke with girlfriend at 6:30 a.m. AT Sunday

The gunman's girlfriend, who escaped after an assault in Portapique on Saturday night and hid in the woods for hours afterward, was a key witness as police tracked the gunman.

She provided details about the suspect, 51-year-old Gabriel Wortman, to police, Campbell said. He said police first spoke with her when she came out of hiding at 6:30 a.m. AT on Sunday.

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Campbell described the assault of the girlfriend as "significant" and said that it could very well have been "a catalyst" to start the chain of events that ended the next day with 22 people dead.

But Campbell said police are not excluding the possibility that the shooting rampage was premeditated.

The woman told police the gunman had a replica RCMP vehicle, a police uniform and weapons, Campbell said. This matched some of what an earlier victim who was shot but survived also told police.

WATCH | RCMP recount woman's escape from gunman:

In the second part of his statement Friday, Supt. Darren Campbell recounts how a woman known to the gunman escaped from him during an assault and hid in the woods. 5:16

Gunman owned several police vehicles

Campbell said residents in the area told police the gunman owned several vehicles that looked like police vehicles and also had multiple police uniforms.

The gunman used a handgun and long guns during his attack. Police said they were able to trace one weapon to Canada but that they think the gunman obtained the other firearms from the United States.

WATCH | Police describe the role a mock police vehicle had in the rampage:

In the third part of his statement Friday, Supt. Darren Campbell says that deadly violence continued 12 hours after the first 911 call came in to police. 2:42

But recovering evidence about a "significant number of weapons" and other police uniforms the gunman owned will be difficult, Campbell said.

The gunman's home in the Portapique area as well as garages and vehicles on the property were torched and completely burned to the ground, he said.

WATCH | RCMP comment on the role a mock RCMP vehicle may have played in the rampage:

Saying it would obviously complicate things, RCMP say the Nova Scotia rampage suspect may have been able to escape the first crime scene by driving a mock RCMP vehicle. 0:51

RCMP officers first arrived in Portapique at 10:26 p.m. AT Saturday in response to 911 calls about shots having been fired.

When they arrived in the area, they spoke with a man who said he was shot by someone in a passing vehicle that looked like a police vehicle.

Officers also found several victims dead on the roadway and several homes that had been set on fire. Campbell said 13 victims were found at seven separate locations in the area.

He described the area as a peaceful community where homes are far apart, set back from the road, and there are no street lights.

Officers refueling at gas station when gunman arrived

Police received a second set of 911 calls on Sunday morning from an area about 60 kilometres away from where the initial attacks happened, before the shooting rampage ended in Enfield.

The gunman, driving a Mazda 3 by this time, pulled up to the Big Stop gas station in the community where members of the tactical team were also refueling in unmarked vehicles.

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There are many ways to acquire former law enforcement vehicles, RCMP say, as they are often sold when they are out of service. 1:32

When one of the officers exited his vehicle, there was "an encounter" with the gunman, Campbell said.

"The gunman was shot and killed by police at 11:26 in the morning," he said.

Campbell also gave more details about how Const. Heidi Stevenson, a 23-year member of the RCMP, died.

He said she was on her way to meet another officer, Const. Chad Morrison. Morrison thought Stevenson was pulling up in her vehicle, but it was actually the gunman, who opened fire and wounded Morrison, Campbell said.

WATCH | Details about the RCMP's dramatic encounters with the suspected gunman:

In the fourth part of his statement Friday, Supt. Darren Campbell tells of the RCMP's dramatic encounters with the suspected gunman. 4:59

While Morrison went to receive medical attention, Stevenson continued driving northbound on Highway 2.

"At that point, both vehicles collided head-on and Const. Stevenson engaged the gunman," Campbell said.

The gunman killed Stevenson and took her firearm. He also set Stevenson's vehicle and his own replica RCMP vehicle on fire, Campbell said.

The gunman then killed a person who had stopped to help and escaped in that person's vehicle.

Campbell said some of the victims of the mass shooting died trying to help others.

"These people are true heroes," he said. "To call this a tragedy would be an understatement."

WATCH | RCMP don't believe suspect had access to police radio during rampage:

Though the suspect in the Nova Scotia rampage had access to a mock police vehicle, RCMP believe encrypted channels would have prevented him from hearing communications on police radio. 0:46

Few new details on shots fired in Lower Onslow

Campbell said he couldn't explain why two police officers opened fire at the fire hall in Lower Onslow, N.S., when the gunman was no longer in the area on Sunday. That event is currently being investigated by the Serious Incident Response Team.

Police have said that trying to answer the question of motive is part of the ongoing investigation into the killings.

Wortman had no criminal record but had previously received a conditional discharge and nine months' probation for assaulting a male victim in 2001. The court records associated with that case reveal little about the incident.

Police said there were three clusters of shooting events Saturday night and into Sunday. (RCMP)

Details have also emerged in recent days about a dispute between Wortman and his uncle over finances related to a property in Portapique that was recently bought by one of the 22 people killed on the weekend.

A judge ultimately ruled in favour of the uncle, despite Wortman's claims that he was still owed money.

If you are seeking mental health support during this time, here are resources available to Nova Scotians.

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