Friday marks four weeks since the hunt for Gabby Petito's then-fiance Brian Laundrie began. Which begs the question: How long could he actually survive in the elements on his own?

Laundrie's parents reported him missing to police in North Port, Florida, on Sept. 17, a few days after he went on a hike at the Carlton Reserve, a sprawling swamp near their home.

Police efforts so far to find Laundrie -- the only person of interest in Petito's disappearance -- have been fruitless. His father even joined in on the search this week.

But as the manhunt was heating up, reported sightings in western North Carolina raised the question of whether or not he was trying to blend in with hikers on the Appalachian Trail.

This week on The Debrief Podcast, Pei-Sze Cheng talked with survival expert and instructor Dave Canterbury, the author of the New York Times bestseller Bushcraft 101, about how -- and how long -- Laundrie might be able to survive in the swamps of Florida or the mountains of North Carolina.

Download this week's episode of The Debrief on Apple Podcasts, Stitcher, Spotify or wherever you listen.

Below is a transcript of Cheng and Canterbury's conversation, lightly edited for clarity and brevity.

Pei-Sze Cheng: So, what do you think? What does it take to survive in these terrains? They've been looking at the Carlton reserve, many times they just went back there with Brian Laundrie's father. What is the likelihood that he has survived in that swamp for this long?

Dave Canterbury: I think a lot of that depends on quite a few variables. Number one, it was rumored that he had a backpack with him.

If he had that backpack and he had some type of supplies with him that he understood how to use to take care of himself  -- Simple things like a water filter that will yield drinkable water for a fairly long period of time. Something that he could get away from the elements and off the ground, like a hammock and a tarp. Some type of a water bottle to carry water over distance, something to start fire if the opportunity arose. All those things would fit into a small backpack.  

Fire could be a problem for him simply because it's so visible. He's got to be careful with that, but he can also stash a small amount of food in a backpack.

If he could fish. Or if he was adapted all around water, he could hunt things like frogs, fish, snakes, turtles to consume. He'd probably have to cook those things, so again, fire is going to be the issue.

However, you could survive for a fairly long time in an environment like that, if you were prepared for sure.

That's amazing. I mean, survival is one thing, but doing it undetected would be another, right?

That’s definitely his worst enemy right now along with his own psychological fears of being caught and being pursued.

You have to think that any normal human being, whether he actually killed someone or not -- if he did, that's playing on his mind as well -- there's going to be a certain amount of guilt involved in that no matter how callous of a person you are.

Combined with the fact that he's being pursued combined with the fact that he's probably tired, probably cold, most nights, he's not in his best mental state. I think he's more apt to make mistakes because of that.

His movement has to be limited to low-light hours where he doesn't have that fear of detection.

I think probably if he's in that swamp somewhere, he's probably smart to stay near water. That way, he's near resources, but also to stay in areas that aren't so clustered with vegetation. If he has to move at night, he can do that safely without tripping over animals different types of vegetation and debris. That would be my guess, if it were me, that's what I would be doing.

Authorities were saying that 75 percent of that reserve is covered in water and that there are poisonous snakes and alligators. Really, what are the odds of being able to survive undetected there?

I think you have to remember that the threat of an alligator is not what most people believe it to be.

Unless you're in nesting season or you stumble across a one is with babies, your chance of outright being attacked by an alligator if you're not in the water anyway are pretty remote. Now venomous snakes, that's a different story. There's lots and lots of venomous snakes in that area.

That area is also infested with mosquitoes. If he doesn't have a way to keep those bugs off of him, that's going to be very traumatic as well over time.

There was one sighting, one particular sighting of him along the Appalachian trail. Do you think it's more likely he'd be able to hide for a much longer time there than in Carlton Reserve?

I do. I think it would be much more likely for him to not only survive, but be more comfortable and move more undetected.

You think about the state that the nation's in now with the threat of COVID and things like that. Brian Laundrie doesn't have many striking features. He's not somebody you'd recognize on the street necessarily, especially if he were wearing a mask in a ball cap.

So if he's walking around the Appalachian trail area, he could very feasibly walk into a town and resupply with a mask on and a ball cap or a hoodie and not be recognized by a local person that didn't recognize his voice.

Then again, there's a lot of hikers on that trail. So you also have the worry of "is somebody going to recognize me?" He's not going to walk around with a mask on 24 hours a day. Maybe he's already been spotted, maybe he hasn't. You know, people see Elvis every day but that doesn't mean he's there.

If he’s on the trail, I think that sooner or later he's going to make the mistake of being spotted by a credible witness and get caught. That’s if he’s still alive.

If you're trying to find your next meal probably takes up most of your day. It's not an easy thing, right?

I think it depends on the environment.

If he's in Florida, he has a much better opportunity to find food. Because there's so much water, there's going to be lots of fish, lots of reptiles, lots of amphibians, lots of things like that to eat that he can find and gather fairly readily if he's careful about it and he knows anything.

The problem with all of that comes down to, “how do I prepare that food?” Is he eating snakes raw? I highly doubt that.

So he's got to be able to cook that food somehow to make it palatable and to cook that food, he has to start fire. That's his biggest issue: he can't start fire without being seen.

Well he wouldn't have that problem on the Appalachian trail, right?

No he would not. Although, it's not common for people to start fires on the Appalachian trail except in small group camps and shelters that are already pre-built. Most Appalachian Trail hikers carry some type of a fuel burning stove that they used to cook just-add-water meals or food that they can eat cold on the fly.

Starting an outright fire in the woods on the Appalachian trail is not a common thing, again, unless you're in a populated group camp area, in which case he takes a big chance on being recognized.

So your money is on the fact that he might be in the Appalachian trail. He's more likely there than in the Carlton Reserve?

My money says he's probably more comfortable there. If he thought I need to go somewhere where I'm going to feel safe, it's more likely that he would have went there.

That doesn't make it fact. It just makes it my personal opinion.

The clock is ticking for him. If he had gotten supplies however many weeks ago, they're probably running low if he hasn't run out, I mean, he's going to have to surface at some point.

If he’s along the Appalachian trail somewhere and has any kind of money, he could just walk into a trail store in a small town in a mask and a ball cap and probably not be recognized.

So it's possible he could even resupply. How many weeks of supplies do you need to hide out? Could you fit everything you need in a backpack?

Again, it depends on whether you're talking about Florida or whether you're talking about the Appalachian trail.

If you're talking about Florida, he has no way to resupply, most likely. If he's in Florida, the clock's ticking and his time's going to run out fairly soon.

The weather's going to change and it's going to start getting colder at night and he's going to run the risk of having hypothermia. He can't keep himself warm without a fire unless he has wool blankets or sleeping bags and all those types of things.

He probably didn't think to take them because he didn't know he'd be on the run this long.

If he's on the Appalachian trail, that's a different story. You can resupply over and over and over again, as long as he doesn't get recognized.

If he's got money, he could just keep bouncing in and out to these trail towns and things like that in small areas and buying more food, buying more supplies, buying whatever he needed. As long as he doesn’t get recognized, he could stay there until he runs out of money.

That's actually a good point. You don't really need to be such a skilled survivalist to live under those circumstances.

Not along the Appalachian trail. I would say no.

The people that walk the Appalachian trail, I would give them all the credit in the world for doing that because it's not an easy feat. However, it is camping. And it is temporary camping because you're going from one town to the next to the next.

A lot of those guys have things mailed to them to post office boxes, where they can go pick that supply up to resupply on things. You can buy new water filters in town. You can buy food. You can buy fuel for a stove. You could buy an additional hammock or under quilt to keep you warm. All those things are available to you in those trail towns, because the Appalachian trail is known for having through hikers.

If he has money, he can buy anything that he needed as long as he didn't get recognized in the process.

Right. So if he has money still to buy these supplies, how much longer do you think he could really be on the run?

Again, I think it depends on how long his money holds out. But it also depends on how long his luck holds out.

Right now that's the thing is probably against him the most is the amount of time he's been on the run and hasn't been recognized by someone credible enough for him to get caught.

I think that the timeframe could be another week. It could be another month. It could be another two months.

But even if he's in North Carolina, by the time December rolls around you're talking about some very cold nights. And that calls for, "I have to have fire. I have to have shelter. I have to have proper clothing."

Those are things that he might not be able to afford to do in the long term. So that may cause him issues. He may have to come out and just surrender, give himself up whatever he decides to do.

But I think he's probably still got at least another month before that's going to become a problem.

Oh, wow. Another month. Okay. Well, thanks for sharing your insights with us, Dave.

Oh, no problem. I hope he gets found pretty soon to tell you the truth.