Police say 2 roommates were home when 4 Idaho students were stabbed to death and don't know why it took hours to call 911

• Two roommates were home at the time four University of Idaho students were stabbed to death, police said.
• A 911 call was not made until hours later and police don't know why it took so long, authorities said.

Two roommates of the four University of Idaho students stabbed to death inside of an off-campus residence over the weekend were home at the time of the killings, authorities said, but 911 wasn't called until hours after they were slain — and police don't know why it took so long.

Cops found Ethan Chapin, 20, Madison Mogen, 21, Xana Kernodle, 20, and 21-year-old Kaylee Goncalves killed inside the home less than a mile from the Moscow, Idaho, college on Sunday just before noon after someone called 911 for a report of an "unconscious" person.

But authorities believe the victims — four friends — were murdered at the home hours earlier by a killer — or killers — who remains on the loose.

"We don't know why that call came in at noon and not in the middle of the night," Moscow Police Chief James Fry told reporters during a Wednesday night press conference.

Fry wouldn't say who called 911, but revealed that two roommates were home at the time of what police have described as an "isolated, targeted attack."

The roommates weren't hurt and Fry refused to say what they told police. Fry suggested that the roommates were not witnesses to the attack.

There were no signs of forced entry, but the door of the residence was open when police arrived at the scene, Fry noted.

Meanwhile, police walked back their earlier assurances that there wasn't a threat to the community, which has been rocked by the killings.

"We do not have a suspect at this time and that individual is still out there," Fry said, adding, "We cannot say that there is no threat to the community and as we have stated, please stay vigilant, report any suspicious activity and be aware of your surroundings at all times."

The FBI and state police are helping investigate the murders.