Washington (AFP) - A month after four university students were stabbed to death in the same house in the US state of Idaho, police have yet to identify a suspect, the internet is lit up with theories from amateur sleuths and the mystery surrounding the crime is deepening.

Just before noon on November 13, police received a call from students at the University of Idaho in the small town of Moscow, set amid hills in the northwestern state.

They rushed to 1122 King Road and found four bodies at the house, two on the ground floor and two more upstairs.

Four young white people have been repeatedly stabbed: Kaylee Goncalves and Madison Mogen, both 21; and Xana Kernodle and Ethan Chapin, both 20 and in a romantic relationship. Police find no evidence of a sex crime. Some of the bodies show wounds suggesting they tried to fight off the attacker.

Police initially said they believed all four were assaulted as they slept, and that the attack somehow did not wake up two other students living in the three-story home.

The crime was committed sometime between 2:52 am -- when the last phone calls from Goncalves' phone were made -- and the time of the emergency calls to police at mid-day. All four students had been partying the night before. It was just another Saturday night on an American university campus.

Fear spreads

A hundred-odd investigators from the local and state police and the FBI are mobilized. Over the course of the probe they go on to collect 113 pieces of physical evidence and take approximately 4,000 crime scene photographs. A tip line set up specifically for the case receives nearly 2,800 calls and a similar number of emails.

But the authorities are flummoxed. 

As of Tuesday December 13, the city of Moscow's website still says tersely, "at this time there are no named suspects, no arrests and no weapon has been found."

But the list of people cleared of suspicion is long: the two housemates that were not attacked; a man in a hoodie who was seen near Goncalves and Mogen as they bought something from a food truck when they came out of a bar around 1:30 am that fateful Sunday morning; the private-party driver who took them home; people who came to the house just before noon to see the roommates who were not attacked; and a man who may have stalked Goncalves months earlier.

With no arrest made in the case, fear spreads on the university campus. Many students go back home to their parents and attend classes online. Police beef up street patrols and security is tightened at local schools.

It doesn't help people's frayed nerves that the authorities have little to say about what happened, or give shifting versions when they do speak out.

The day after the murders, for instance, Moscow Mayor Art Begge called them "a crime of passion." But then he walked this back.

The next day the police said they believed it was "an isolated, targeted attack" and there was no imminent threat to the community. Then they backpedaled again and spoke evasively.

Only this past Saturday police urged people in Moscow "to stay vigilant, travel in groups, and communicate with family and friends as you travel."

And investigators have avoided making public certain details of the investigation, such as where exactly the bodies were found; where specifically they were stabbed; what prints and DNA samples have been collected; and what was the tone of the first emergency call the morning the bodies were found.

Rumor mill

These unanswered questions have given rise to all kinds of speculation, especially online.

On the online forum Reddit, would-be detectives dissect surveillance video from outside that food truck where Goncalves and Mogen got something to eat after coming out of the bar. 

Some zero in on the nearby man in the hoodie, saying he looks suspicious, even though police have ruled him out as being the assailant.

Others online say it must be the work of a serial killer.

There are calls to raise money so one of the bereaved families can hire a private detective.

Then there is the issue of a white Hyundai that police say they are looking for. On a Facebook group with some 75,000 members that is dedicated to this crime, one commentator linked the vehicle to a robbery committed several days before the students murders and told the FBI about it. That theory elicited 996 comments from other people.

Local police got so many calls about this car they ended up re-routing them to an FBI call center.

And most of the police press releases about the investigation now have the purpose of ruling out far-fetched theories about the crime.