the surviving housemate heard someone say "I am going to help you" minutes before seeing a masked figure creep from the property where four students were brutally killed.

The chilling revelations cames as suspect Bryan Kohberger appeared in Idaho court for the first time charged with the horrific murder of four University of Idaho students, stabbed to death in their beds.

The arrest affidavit, a document detailing a summary of the evidence and the circumstances of the arrest, revealed new details about the case that has terrified and captivated the country.

Kohberger, 28, a criminology student, was arrested on Friday December 30, six weeks after four students were stabbed to death in their Moscow, Idaho, US, rental student home.

The bodies of Madison Mogen, 21, Kaylee Goncalves, 21, Xana Kernodle, 20 and Ethan Chapin, 20, were found stabbed to death in their beds.

Key revelations from the affidavit include:

• One of the surviving housemates saw a masked figure in the house the night of the killings
• A knife sheath suspected to have traces of Kohberger's DNA was found at the scene by the bodies of two of the victims
• Authorities were investigating Kohberger by November 25, over a month before his arrest

• Kohberger's mobile phone was near the victims’ home 12 times prior to the killings

Key questions still remain unanswered though, including whether the suspect and any of the victims knew each other, and why police weren’t called until nearly eight hours after the killings likely occurred.

She told investigators that she was awoken by noises at about 4am, and thought she heard another housemate say something like, “there’s someone here.” She looked outside her bedroom and didn’t see anything.

Later she thought she heard crying coming from Kernodle’s room and looked outside again. That’s when she said she heard a male voice say something to the effect of, “it’s OK, I’m going to help you,” according to the affidavit.

She later opened her door a third time and saw a masked man in black clothing whom she did not recognise walking toward her and stood in “frozen shock” as he walked past her toward a sliding glass door, the affidavit said. She went back in her room and locked the door.

Investigators believe the suspect then left the home

Traces of a man's DNA later determined to be Kohberger were found on the button of a leather knife sheath found at the murder scene, according to the affidavit written by Brett Payne, a police corporal in Moscow.

It was found alongside the bodies of Goncalves and Mogen.

Investigators later closely matched the DNA on the sheath to DNA found in rubbish taken from Kohberger’s parents’ home in Pennsylvania, where he was arrested last week.

The sheath had a U.S. Marine Corps insignia on it, though there’s no record of Kohberger having served in the military.