The Nova Scotia gunman who killed 22 people in one of Canada's worst mass shootings evaded police for nearly 13 hours by driving through a field, spending the night in an industrial area and changing his clothes and vehicles several times.

The gunman was disguised as a police officer, wearing parts of an authentic RCMP uniform and driving a replica RCMP car during part of the shooting rampage that began on the night of April 18 in Portapique, N.S.

WATCH | RCMP say N.S. gunman wore parts of authentic uniform

Supt. Darren Campbell outlines the timeline of the N.S. shooter's deadly rampage 3:35

Over the next 13 hours, he killed strangers and people he knew before being shot dead by police nearly 100 kilometres away from where the first shots were fired.

Nova Scotia RCMP provided many more details on the gunman's movements on the night of April 18 and the morning of April 19 during a news conference on Tuesday.

WATCH | RCMP say gunman left the Portapique area by driving through a field

Supt. Darren Campbell gives an update on investigation into mass shooting 2:10

Supt. Darren Campbell also said the gunman was related to retired RCMP officers.

But Campbell added that there is no indication at this time that any former members of the RCMP helped the gunman or provided him with a police uniform or RCMP vehicle.

"Though the gunman will never stand trial, we still have a duty to complete this investigation by the same standards that we would have if he was standing trial," Campbell said.

911 call

Police initially didn't say when the first 911 call came in, but Campbell said Tuesday that it was around 10 p.m. local time on April 18.

Police say 51-year-old Gabriel Wortman killed his first victims in Portapique. He then left the small seaside community by driving through a field at around 10:35 p.m., just minutes after police arrived in the area, where they found dead bodies on the road and several homes on fire.

He drove about 26 kilometres east and arrived in Debert around 11:12 p.m., Campbell said.

The gunman hid out in the industrial area for more than six hours before resuming his rampage. Police have searched the area in Debert but they don't know exactly what the gunman did while he was there.

"We are making a plea to anyone in that area if they saw anything suspicious to please contact police," Campbell said.

RCMP investigators search for evidence at the location where Const. Heidi Stevenson was killed along the highway in Shubenacadie, N.S. (Andrew Vaughan/The Canadian Press)

Police do know that he left the area around 5:43 a.m. the next day and went toward Wentworth, Campbell said.

CBC News has compiled a timeline of what we know so far based on information from RCMP, audio recordings of scanner traffic and interviews.

435 witnesses

Campbell said police officers have spoken with the gunman's girlfriend, whom he called a "critical witness," and expect to interview her many more times.

The woman was attacked and forcibly restrained by the gunman, but managed to escape and hide overnight in the woods. She provided key details to police, including that Wortman was driving a mock RCMP cruiser and was disguised as a police officer.

A virtual vigil was held on Friday to mourn the 22 people killed during one of the deadliest mass killings in Canadian history. (Andrew Vaughan/The Canadian Press)

RCMP said the remains of eight victims were recovered from burned structures and vehicles. They have not confirmed the cause of death for 14 others. Three people were injured, including a police officer.

"We know there are no other victims," Campbell said Tuesday.

The investigation, which required sifting through 16 crime scenes, is a colossal undertaking, experts say.

But Campbell said police are making "significant progress." Police are still on scene at five locations but the rest have been released, he said.

Police have been piecing together the events of that night, as well as tracking Wortman's prior activities, through search warrants and searches of records, video evidence and interviews with witnesses. Campbell said police have identified 435 witnesses and have interviewed more than half of them.

He said police have also been working with the Canada Border Services Agency. Campbell previously said that police believe the gunman obtained some of the weapons he used from the U.S.

Campbell said the gunman had several semi-automatic handguns and two semi-automatic rifles but didn't say whether he held any firearms licences.

Asked about explosions reported by some witnesses, Campbell said witnesses have told police that Wortman possessed a "significant amount" of ammunition and some of it may have ignited and exploded as homes were burning. Wortman also wounded or killed "animals and pets" at the homes where people were killed.

Where did gunman get RCMP uniform?

A key part of the police investigation is how the gunman obtained parts of an authentic RCMP uniform, including a shirt and pants with a yellow stripe.

"We have yet to confirm exactly where or how he obtained these uniform pieces. That's an important aspect of our investigation and this will take some time," Campbell said.

WATCH | N.S. gunman hid from police, changed clothes, cars during rampage:

Nova Scotia RCMP say the gunman in the mass shooting earlier this month initially fled through a field, hid from police and changed clothes and cars several times during the rampage. 2:05

He also had four replica police cars, which Campbell said were all former police models that had been acquired through auctions within the past few years.

The replica RCMP car that he drove during part of the rampage was purchased in the fall of 2019, and the gunman outfitted it with a light bar and decals, Campbell said.

WATCH | Remembering the victims of Nova Scotia's mass shooting

In memory of the 22 people who lost their lives in the mass shooting in Nova Scotia. 3:56

The victims of one of Canada's deadliest mass killings were remembered on Friday night during a virtual vigil that included a moving fiddle duet by Natalie MacMaster and a clip of the youngest victim, 17-year-old Emily Tuck.

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