The hunt for a killer responsible for the grisly murders of four University of Idaho students has taken investigators over the border into the neighbouring US state of Oregon.

It is there that a killer in a mask snuck into the bedroom of married couple Travis and Jamilyn Juetten sometime after 3am on August 13 last year and stabbed Jamilyn 19 times.

The 24-year-old survived the brutal attack, but her husband died trying to save her.

Details of the crime have been pored over by amateur sleuths because of similarities to the recent murders in Moscow, Idaho, that claimed the lives of Kaylee Goncalves, 21, Madison Mogen, 21, Xana Kernodle, 20, and Ethan Chapin, 20, on November 13.

The attacks, which took place 640km apart, were both carried out as the victims slept in their beds.

Eerily, the killer or killers spared the lives of other occupants in the home.

At the share house where the four students were murdered last month, two housemates slept through the entire massacre.

In Salem, Oregon, where Jamilyn and Travis Juetten were attacked, a third person was also sleeping nearby.

Authorities said the couple were planning a trip to Hawaii the following day and a person who was going to cat-sit for them was sleeping in another room.

Moscow Police Chief James Fry, who is the face of the hunt for the University of Idaho killer, told reporters he is “looking into any possible connection” between the attacks.

• 'Isolated attack': Four Idaho students mysteriously found dead

The four University of Idaho students who were found dead in off-campus housing were identified on Monday as Madison Mogen, 21 (top left), Kaylee Goncalves, 21 (bottom left), Ethan Chapin, 20, and Xana Kernodle, 20. They are pictured just hours before their untimely deaths. Photo / via Instagram

“We’re looking at every avenue and we have other agencies reaching out to us with other cases and stuff that we are going to follow up on those,” Chief Fry said.

The mother of Travis Juetten said it would be the “best Christmas present ever” if police were able to link the cases and find one killer.

“I want answers for all five of them,” Myra Juetten told The Independent.

Juetten said she was surprised when she heard the police chief’s comments because she had not been contacted by police in Idaho.

“I heard it on the news conference the other day that they were exploring it or that they were aware of it – that was the first I knew,” she said.

“I did get my hopes up as it’s been a year and a half and we have nothing.”

The possible link comes as police probe all possible scenarios.

The three women who were stabbed to death shared a house together off-campus. The fourth victim, Ethan Chapin, was visiting his girlfriend, Kernodle.

Police have been quiet about crime scene specifics to protect the integrity of their ongoing investigation. However, on Friday, investigators clarified some details in an interview with Fox News Digital.

 “When the chief said that [the slayings were targeted], and [investigators] still believe that now, it didn’t appear that there was any forced entry into the residence,” Idaho State Police communications director Aaron Snell said.

“There were survivors of this. And then as well, based on the evidence internally at the scene, that has led detectives to believe and continue to believe that this was a targeted event.”

He declined to discuss what evidence was recovered at the scene or to identify who and how many of the victims specifically the killer was targeting.

In a televised interview, Steve Goncalves, father of victim Kaylee, told CNN that he had been informed that there was only one target among the four victims. Separately, he told Fox News last week that the attacker had been “sloppy” and left behind an abundance of evidence.