Sheriff Chris Fitzgerald said Wednesday that he believed Jayme Closs was in the room when James and Denise Closs were shot to death.
Closs' parents were fatally shot and their deaths have been ruled homicides, Fitzgerald said Wednesday.
Fitzgerald has yet to say how long the parents were dead before the bodies were discovered after the 911 call brought deputies to the home, which is set back in woods along Highway 8 just west of town.
Fitzgerald said investigators still have a "100 percent expectation that she's alive", but that even though they've received more than 400 tips, none have been of a credible sighting. Meanwhile, authorities say they've gotten more than 200 tips following an Amber Alert that was issued Monday afternoon.
Barron Area School District administrator Diane Tremblay said Jayme, a member of her school's cross-country team, is a "sweet girl who is a loyal friend and loves to dance".
During a media briefing on Tuesday morning, Fitzgerald said that he can't reveal why authorities believe Closs is in danger because it could compromise the investigation. He also dismissed the idea Jayme had run away from her home in Barron, located about 80 miles northeast of Minneapolis.
The tragedy unfolded about 1 a.m. Monday with a cryptic 911 call to police. Jayme was at a family gathering Sunday afternoon.
"We are also hopeful for the safe return of their daughter, Jayme, and are keeping her and the Closs family in our thoughts".
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According to the National Centre on Addiction and Substance Abuse, 90 per cent of addiction begins in adolescence. But there remain concerns, including about the readiness for police forces to tackle drug-impaired driving.
"That's part of the investigation", Fitzgerald said.
"I'll be honest. I'm struggling with this because I don't have some of those answers that I want to give you", Fitzgerald told reporters. He has said she is not a suspect in her parents' deaths and said she's not a runaway.
Naiberg, Denise Closs' father, told The Associated Press on Tuesday that Jayme "was quiet as always" at his grandson's birthday party.
"Is it a random attack or is it a targeted attack?"
"Every second counts in this case", he added.
While 82 percent of the Amber Alerts issued previous year identified a vehicle and 50 percent had specific license plate numbers, according to U.S. Department of Justice statistics, Closs' case offers neither of those clues. Additionally, he said people may have information and not even realize it.
The FBI and the National Center for Missing and Exploited Children are helping in the search.
The missing teenager has been described as being approximately 5ft (1.5m) tall and 100lb (45kg) with green eyes and strawberry blonde hair. Sheriff Fitzgerald urged the public to continue calling the hotline with tips: 855-744-3879.