It’s one of the worst mass killings in Canadian history, and as communities on the East Coast grieve, the search for answers continues.

RCMP are investigating last weekend’s shootings in northern Nova Scotia that claimed the lives of at least 22 people, including one of the police force’s constables, and ended with the death of the shooter in a confronation with police.

Here is some of what we know so far — as well as some of the key questions that remain unanswered.

What happened — and when

At 10:36 p.m. on Saturday, RCMP responded to “a firearms complaint” in Portapique, N.S. There, officers found “multiple casualties” both inside and outside of the home — but no shooter. They also discovered fires and more victims in the area.

From midnight until around 8 a.m. on Sunday, the shooter’s whereabouts remain unclear. That part of the timeline has become a subject of much scrutiny as the public tries to understand how one person could have eluded police for so long and caused so much death and destruction.

Between 7 a.m. and 8 a.m. Sunday, RCMP said, they spoke to a witness that let them know Wortman was driving a near-exact replica of an RCMP.

At 8 a.m. Sunday, RCMP described the investigation as an "active shooter situation," telling residents to stay in their homes.

An hour later, the shooter’s description and picture were released to the public via Twitter.

At 10:17 a.m., a picture of Wortman’s RCMP look-alike car was tweeted out by the RCMP.

Around 11:30 a.m., the gunman was killed in a confrontation with police at the Big Stop in Enfield, N.S. — a big, province-famous gas station in Nova Scotia.

The RCMP said Wednesday they could release a full timeline of events as early as Thursday.

Did the shooter have an accomplice?

On Wednesday, RCMP said in a news conference the shooter acted alone on Saturday night and Sunday morning.

However, police say they’re investigating whether anyone helped the shooter with his actions in the lead-up to the crime.

Did RCMP make the wrong decision on alerting residents?

Controversy looms over the RCMP’s decision to rely on Twitter rather than the province’s emergency alert system to warn the public that the gunman was still on the loose.

On Wednesday, RCMP Chief Supt. Chris Leather told reporters that officials from Nova Scotia’s emergency management system told the RCMP at 10:15 a.m. on Sunday that they could issue an alert if necessary.

The RCMP, said Leather, spent the next hour or so tracking down the relevant officials, and consulting on whether the alert was necesssary. While they were drafting the alert, the gunman was killed — around 11:30 a.m. Sunday.

Nova Scotia Premier Stephen McNeil told CTV Atlantic this week that more could have been done.

“I would say (with) the benefit of hindsight, the depth and breadth of this should have been communicated more widely with a number of our agencies,” he said. “But let’s let that unfold. My main focus right now is to support those families.”

Who were the victims?

RCMP confirmed Tuesday afternoon that 22 people, plus the gunman, are dead following the incident.

Identified as victims so far are:

RCMP Const. Heidi Stevenson, a 23-year member of the national police force and a mother of two;

Debert Elementary school teacher Lisa McCully;

Gina Goulet — Denturist;

Care assistant Kristen Beaton;

Heather O’Brien, a nurse from Truro;

Peter and Joy Bond, a couple in Portapique with two sons;

Couple Dawn Madsen and Frank Gulenchyn;

Retired firefighter Tom Bagley;

Parents Aaron Tuck, Jolene Oliver, and daughter Emily Tuck;

Couple Greg and Jamie Blair;

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Sean McLeod and Alanna Jenkins — Correctional officers;

Lillian Hyslop;

Corrie Ellison;

Couple John Zahl and Elizabeth Joanne Thomas (presumed dead).

Who was the shooter?

Gabriel Wortman, 51, a denturist with an office in Dartmouth, N.S.

Where did the shooter get his RCMP uniform and cruiser?

Donald Walker’s family hired the shooter in the ’90s to work in their funeral home business before he switched careers to become a denturist. Walker told the Star Wortman acquired many items from a local auction house that sells Crown assets and used a local detail shop to apply the graphics and decals. He said Wortman told him last year that RCMP were aware of his replica vehicle and had advised him that if he planned to take it onto the highway he would need to transport it on a trailer.

Police confirmed Tuesday that the shooter was wearing an “authentic police uniform.” The force did not indicate how he came to acquire the uniform and did not respond to the Star’s inquiries about it.

Retired RCMP deputy commissioner Peter German said it’s possible to purchase uniforms online through military surplus-style stores. While sites like eBay do not permit the sale of uniforms, they do allow the sale of items like police patches. It is also possible that it was a discarded uniform. When Mounties retire they’re expected to turn in their uniforms or destroy them, he said. Yet another possibility is that the uniform was acquired from a collector.

The thing to keep in mind, German said, is that possession is not illegal; it’s the act of impersonating an officer that is illegal.

Is there any explanation yet for the killer’s actions?

Police have said the killings appeared to be, “at least in part, very random in nature.” However there have also been other signs, that might suggest premeditation, including Wortman’s donning of the police attire and vehicle.

RCMP said Tuesday that, “Some of the victims were known to Gabriel Wortman and were targeted while others were not known to him. We will not be providing more information on how the victims may have been known to Gabriel Wortman.”

What has the response been?

The community of Portapique and the province of Nova Scotia have seen an outpouring of online support in the wake of the unprecedented mass shooting, with social media users posting #NovaScotiaStrong messages Sunday and Monday.

Community members have been posting tributes about the people who lost their lives. In the morning hours, several people lined up along the road near an RCMP station, practising social distancing at the same time, to show their support.

Nova Scotians, and others across Canada, lit candles Monday evening in grieving. Nova Scotia flags have also been unfurled and flown from porches and flagpoles across the province in a show of solidarity.

The N.S. RCMP also launched an online condolences platform for the family and friends of Const. Heidi Stevenson, which can be accessed here.

What happens now?

RCMP are continuing their investigation into what happened. There are 16 crime scenes scattered across the province relating to the shootings, according to the RCMP.

The province’s police watchdog is also involved. The Serious Incident Response Team has taken over the investigation of the shooting of the suspect, in addition to another incident related to the manhunt, according to the RCMP.

“The province's independent Serious Incident Response Team (SiRT) will investigate the circumstances surrounding the discharge of firearms by two members of the RCMP. This is an additional referral from the RCMP,” SiRT said in a news release Monday. The circumstances of this investigation have not been explained further by SiRT or the RCMP.

That team is responsible for investigating all serious incidents involving police in Nova Scotia, whether or not there is an allegation of wrongdoing. A public report into the incident must be filed within three months, after it is finished.

With files from Douglas Quan, Evelyn Kwong and Star Staff.