MOSCOW, Idaho -- More than 100 investigators, officers and support staff have fielded about 600 tips since the murders last week of four University of Idaho students, officials said on Sunday.
As the tips pour in, each has been processed, vetted and cleared, according to the Moscow Police Department, which has five support staff members dedicated to the case.
"Thirty-eight interviews have been conducted with individuals who may have information about the murders," the department said in a Sunday briefing update.
Investigators have released timelines detailing the whereabouts of the victims and the other students who lived at the off-campus house. No arrests have been made by authorities.
Investigators said they've also conducted autopsies and have searched for surveillance video. They've asked for tips from anyone "who observed suspicious behavior."
"Currently, no suspects are in custody and no weapon has been located," investigators said.
The victims who were found dead on Nov. 13 have been identified as Ethan Chapin, 20, of Conway, Washington; Madison Mogen, 21, of Coeur d'Alene, Idaho; Xana Kernodle, 20, of Avondale, Arizona; and Kaylee Goncalves, 21, of Rathdrum, Idaho.
ABC News contributor and former FBI agent Brad Garrett told "Good Morning America" on Monday that the killer or killers may have been familiar with the layout of the house.
"It tells me that someone came into the house with a comfort level -- that they probably knew their way around the house," Garrett said.
The Moscow Police Department said it has dedicated four detectives, 24 patrol officers and five members of its support staff to the investigation. They've been joined by a wave of outside investigators, who've taken over Moscow, a college town with about 25,000 residents, since the killings were first discovered last Sunday.
The FBI sent 22 investigators to Moscow, according to the local police. Another 20 agents were working on the case but located in Treasure Valley, Idaho; Salt Lake City, Utah; and West Virginia. Two members of an FBI behavior analysis unit were also working on the case, police said.
Investigators also said a 911 call came from inside the residence and was made on one of the surviving roommates' cellphones. They initially told authorities that someone was passed out and wouldn't wake up, officials said.
"Multiple people talked with the 911 dispatcher before a Moscow Police officer arrived at the location," officials said. "Officers entered the residence and found the four victims on the second and third floors."
Garrett said investigators should be broadening their search outside the victims' immediate circle of friends and family.
"You're going to have to start spreading out to people they had just a casual relationship with," he said.
ABC News' Emily Shapiro, Melissa Gaffney, Marilyn Heck, Izzy Alvarez and Flor Tolentino contributed to this report.