Gabby Petito's Best Friend Says Brian Laundrie Is Capable of Surviving in the Wilderness

Brian Laundrie, who was reportedly last seen on Sept. 14, is capable of surviving on his own, according to Gabby Petito's best friend, Rose Davis.

"He is out in the wilderness, I promise you," Davis, 21, tells PEOPLE, noting this is not the first time he's lived in the wild on his own.

"He's out there. He is," Davis insists. "If he's alive, he's out there, camping out ... He lived in the Appalachians by himself for months."

This morning, the search for Laundrie continued in Carlton Reserve, a 25,000-acre nature reserve consisting primarily of swampy wetlands.

The 23-year-old reportedly left last week for a nature hike and has not been seen since.

Petito's body was recovered over the weekend from Wyoming's Grand Teton National Park. She was first reported missing by her mother on Sept. 11 — 10 days after Laundrie returned to his parents' home in North Port, Fla., in the white van he and Gabby had been using to travel the country.

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Authorities say her death was a homicide.

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Laundrie returned alone, authorities have said. He has refused to sit with investigators to discuss the case.

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"This is a very heartbreaking tragedy," Davis says. "It is so surreal. It is so just horrific. There's almost a loss of words for it because no one deserves to go out this way, especially not her."

Davis tells PEOPLE she has been talking to police and FBI agents, telling them everything she knows about Laundrie. She suspects he is on the run, in the swamps, and not holed up with someone who might be harboring him.

"He does not have friends," Davis said. "He reads books."

According to Davis, she became friends with Laundrie, too, as her friendship with Petito, 22, blossomed.

"You don't know what it's like for someone you considered a friend to murder your best friend," she says. "I've stayed at their house. I've slept in the same house as him. I ate dinners with him, played board games with him, gone to the beach — even though he didn't really hang out with us at the beach — but going to the beach with him. That's scary."

On Sept. 15 Laundrie, now a fugitive from the law, was named a person of interest in Petito's disappearance. Laundrie has not, however, been identified as a suspect in his fiancée's death.

When he vanished, sparking a massive manhunt utilizing drones, divers, and search dogs, Davis says she was nervous that Laundrie would show up at her house.

"He knows where I live," Davis explains. "When he first went missing, there was a small percentage of me that was like, he definitely knows where I live. And he does not like me."