Canadian police said Wednesday they are scaling down but not abandoning the hunt in a remote and rugged part of northern Manitoba for two teenagers suspected of killing a college professor, a North Carolina woman and her Australian boyfriend.

Over the last nine days, police and others have used helicopters, drones, boats and dogs to search approximately 4,200 sq miles (11,000 sq km) of tundra, muskeg and dense forests. At one point a military Hercules aircraft was used in the search, which has stretched across three provinces.

Kam McLeod, 19, and Bryer Schmegelsky, 18 are considered main suspects in two murders. Photograph: -/AFP/Getty Images

“To be clear, we’re not ending the search,” said Jane MacLatchy, the Royal Canadian Mounted Police assistant commissioner, at a news conference in Winnipeg.

“I know that today’s news is not what the families of the victims and the communities of northern Manitoba wanted to hear. But when searching for people in vast, remote and rugged locations, it is always a possibility that they are not immediately located,” she said.

Over the next week there will be a phased withdrawal of RCMP and military personnel and assets from the Gillam area, about 660 miles (1,100km) north of Winnipeg, where a burnt out vehicle belonging to the suspects was found last week. MacLatchy wouldn’t say how many officers will remain involved in the search.

Military aircraft that were helping with the search have pulled out, she said. And a number of tactical resources and specialized assets will remain in the Gillam area and police are ready to return if needed.

Nineteen-year-old Kam McLeod and 18-year-old Bryer Schmegelsky have been charged with second-degree murder in the death of Leonard Dyck, a University of British Columbia professor whose body was found last week in British Columbia.

They are also suspects in the fatal shootings of Australian Lucas Fowler and Chynna Deese of Charlotte, North Carolina, whose bodies were found on 15 July along the Alaska Highway about 300 miles (500km) from where Dyck was killed.

The search for them – which has involved the canvassing of over 500 homes and buildings and the following up on over 250 tips – has left some residents scared and on edge.

“However, even with this extraordinary effort, we have not had any confirmed sightings of the suspects since the burned vehicle was located,” MacLathcy said. “Taking into account all of the work so far, it has come time to re-assess our deployment of resources to the area.”

There is a possibility the suspects had some sort of assistance in fleeing the area, MacLatchy said. There’s also a possibility they could be dead.

“Everything is possible at this stage,” she said. “The north part of the province is a very unforgiving place. We are keeping all possibilities in mind as we go forward.”

On Tuesday, police abandoned their search for the pair in York Landing, a small community near Gillam. The search was prompted by a tip from a neighborhood watch group, but police said there were no sign of the teenagers.

MacLatchy has “no regrets” over how the search was conducted.

“This is a very large area we are looking at, very remote,” she said. “It’s a very tough place to find somebody who doesn’t want to be found.”

Earlier in the manhunt, Schmegelsky’s father, Alan Schmegelsky, said he expected the nationwide manhunt to end in the death of his son, who he said is on “a suicide mission”.