• The search for Brian Laundrie entered its fourth week Monday
  • Teton County coroner will provide an update on Gabby Petito's autopsy report Tuesday
  • Petito's body was found on Sept. 19 at a Wyoming campground

As the search for Brian Laundrie entered its fourth week, a survival expert and star of the show “Lone Target” talked about the most important factors keeping Gabby Petito's fiancé alive if he was hiding out in the wilderness.

Joel Lambert, also a former Navy SEAL, told Ashleigh Banfield of News Nation that Laundrie's mental fortitude was the main focus for him now.

“Your mental mindset is the most important tool and it could also be your worst enemy,” Lambert said as he broke down what Laundrie might be experiencing each week while on the run. Lambert explained during his first week his focus is a rule of threes.

“Rule of threes states that you can survive three hours without shelter, you can survive three days without water, and you can survive three weeks without food,” Lambert said.

During week two, adrenaline can impact the four Fs -- fight, flight, freeze and focus.

“With training, an adrenaline response can also be a very positive thing that focuses you against the threat or against whatever it is that you’re dealing with,” Lambert said.

The third week likely comprised stressing about food.

“If he’s brought food with him, he’s going to be starting to run low and he’s probably been rationing it,” Lambert said. “And so he’s, like I said, (he would experience a) caloric deficit. And that’s going to be affecting all the aspects of his mind and his body.”

During week four, Lambert says Laundrie is fighting his own mind.

“If your mindset isn’t... focused and sharp and conditioned, then your mind is going to cause the cracks that’s going to break everything down,” Lambert said. “Even if he’s innocent, he knows that... he’s being hunted and he can’t go home and he’s on the run. That’s the kind of thing that’s going to weigh very heavy on someone’s mind and it’s going to drag him down and I think that you may see a mental collapse before too long and maybe... like suicide by cop, he might do something very stupid in order to get caught because he just wants to it all to be over.”

Laundrie – who is the only one named as a person of interest in the case – has been missing. A federal arrest warrant was issued against Laundrie on Sept. 22. His fiancée's body was found on Sept. 19 at a Wyoming campground.

As the case garners nationwide attention, all are awaiting the release of Petito's autopsy report that could shed light into what had happened to her and how she was killed. The coroner of Teton County, Wyoming, will hold a virtual press conference Tuesday to provide an update on the final autopsy report of Petito.

Meanwhile, the search for Laundrie continues with no concrete clues about his whereabouts.

Gabby Petito
Footage from a family travel vlog may have helped provide clues that led to recovering human remains at the Grand Teton National Park. In photo: A makeshift memorial dedicated to missing woman Gabby Petito is located near City Hall on September 20, 2021 in North Port, Florida Octavio Jones/Getty Images