The grey house with the Christmas wreath on the front door and twinkling fairy lights overhanging the back patio could be any other student home in the remote town of Moscow, Idaho.

A blanket of snow covers the ground, and a rubbish bag overflowing with beer and seltzer cans is propped up near an outdoor grill.

The young women who lived here until recently were popular members of sororities at the University of Idaho and regularly threw parties.

They documented their lives on social media, with choreographed videos of group dances and photographs dressing up for nights out.

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But four weeks ago this apparent student idyll was shattered when three of the housemates – Kaylee Goncalves, Maddie Mogen and Xana Kernodle, and Xana’s boyfriend Ethan Chapin – were brutally murdered.

In the early hours of a Sunday morning, as they slept in bed, they were stabbed to death with a large knife, their rooms splattered with blood, while two other housemates slept through the attacks.

Four weeks on, no known witnesses have come forward, there is no named suspect, no murder weapon and no obvious motive.

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Moscow’s small police force, which hadn’t had a murder for more than seven years, is at the centre of the race to find a killer, or killers.

“It’s hard to tell when or if this town will ever be the same,” Robbie Johnson, the force’s public information officer, says.

‘We can’t afford to make a mistake’

There are signs that the community and grief stricken parents of the victims are growing frustrated with what they perceive as a lack of progress by police, even as reinforcements from the FBI and Idaho state police have arrived.

The decision to withhold certain information or lines of investigation from the public is deliberate, Ms Johnson tells Sky News.

“We don’t just want an arrest, we want to take it to court,” she adds.

“We need to be sure we are going through all the evidence and it is vast. There are pictures, emails, phone calls coming in. We can’t afford a mistake or to put out information that might compromise the investigation.”

Police have consistently stated their belief that either the house, or its occupants, were targeted, but they haven’t revealed why they believe that.

The house where they were slaughtered

Internet sleuths have pored over the layout of the building. The ground floor, with its sliding patio doors, is where Xana and Ethan, a couple since the spring who were said to be perfect for each other, were slaughtered.

In one of the bedrooms upstairs, lifelong best friends, Kaylee and Maddie, were also sharing a bed when they were murdered.

In the early hours, they had been repeatedly texting Kaylee’s former boyfriend, with whom she was still close and police have discounted as a suspect.

One of the most puzzling aspects of the case is that two other female housemates, Dylan Mortensen and Bethany Funke, who were in basement level bedrooms, survived.

They say they slept through the attacks and when they woke they summoned other friends to the house, believing one of the housemates to be unconscious.

Just before midday, one of the friends called police, who discovered the true horror of what had happened. Police have discounted Dylan, Bethany and the friends who arrived that morning as suspects.

“The big question is why,” says Troy Lambert, a crime writer whose stepson lives in an apartment less than 100 yards from the murder house.

“Why would they target young college kids who, in my mind would have no enemies,” he adds.

“My stepson and his housemate do gaming and stuff like that, so they didn’t hear anything.

“With the density of students in this area, it is kind of surprising that nobody heard anything. It’s what makes me think that it was somebody and something organised because they didn’t make noise. They knew not to make noise.”

The movements of Kaylee and Maddie

Investigators say they’re busy piecing together not just what happened inside the house, but where the victims had been in the hours leading up to the murders.

Kaylee and Maddie had spent the night at a bar called Corner Club with its neon yellow sign and affordable drinks, just off the main street in Moscow.

They left at 1am to walk to a nearby food truck, where Kaylee can be heard on a livestream, stumbling over her words as she orders a portion of pasta carbonara.

There then appears to be a dispute with a man in a hoodie. At one point, Maddie gestures towards him and seems to say “f*** you mister,” before they all disappear out of shot.

Police say they have also discounted him as a suspect.

It had previously been reported that Kaylee’s parents believed she may have been the primary target based on what they had been told about the extent of her injuries compared with the other victims.

But they now don’t think that is the case.

“I don’t think that the family believes that there was an individual target on their daughter,” their lawyer, Shanon Gray, tells Sky News.

“It just doesn’t make sense with the facts that have been presented and other information that we’ve gathered.

“The person might have targeted the home, because there were all girls that lived there and a lot of people came and went, it was a very social scene.”

Five-page-long list of questions

The Goncalves family recruited Mr Gray to push the police for answers. He took a five-page-long list of questions to a meeting with investigators this week, but they are remaining tight-lipped.

“We asked why they haven’t released more information to the public,” he added. “Down the road we may look at it and say, ‘great job not releasing that information’, or they may come to regret those decisions.

“I don’t know if anyone has ever experienced handling a murder investigation that involves four college students that had been stabbed, so I’m sure it’s new to them.

“But they still need to make sure that they’re doing the right things, and we’re here to hold them accountable for it.”

The missing five hours

Mystery surrounds the whereabouts of the other two victims, Xana Kernodle and Ethan Chapin on the night of the killings.

Between 8-9pm they were at a party at the imposing Sigma Chi fraternity house, with its basketball court in the garden and stars and stripes flag, now flying at half-mast.

It is less than a five-minute walk through an alley to the house where they were killed, but they didn’t reach home until just before 2am and police are trying to account for those missing five hours.

In a sea of uncertainty, a violent killer, or killers, on the loose continues to terrorise this town of 25,000 people, which includes 11,000 students.

Everything that happens in Moscow at the moment is coloured by loss and fear. At winter graduation, where Kaylee Goncalves was supposed to receive her degree, a swell of police patrol the arena.

‘It’s scary being here’

“I have pepper spray and different self-help things, but it’s scary being here, and it doesn’t feel like home anymore. It doesn’t feel safe,” says Emma Bartlett, a graduate, who went to junior school with Kaylee and Maddie and tutored Ethan at university.

“He was always smiling, so happy, so funny,” she says, “I’m just so glad I got to know him.”

It’s not just students who are living in fear. Treva Adkins visited Moscow to see her daughter Katie graduate over the weekend.

“When we checked into the Airbnb, I was scared to death,” she says. “I made my husband check under then bed, and I’m a 43-year-old woman.

“I noticed the windows weren’t locked, and it paralysed me, so I shut all the windows and I closed the curtains. It’s terrifying, constantly looking over your shoulder.”

The lighting of Moscow’s town Christmas tree took place last week and has become a focal point to remember the four slain students. Coloured ribbons are fastened around the guard rails and notes of reflection.

“Gone too soon, Ethan, Xana, Kaylee and Madison,” reads one. “Praying for your family, friends and for justice,” reads another.

In a community desperate for answers and accountability, the unknowns keep stacking up.