What is the Carlton Reserve, the vast swampland where Brian Laundrie is possibly hiding out?

Speculation about Brian Laundrie's whereabouts has circulated online for weeks, with wannabe-sleuths placing him in Mexico, Canada, at least four states, and buried in a bunker under his parents' back garden.

Mr Laundrie is a person of interest in the disappearance and death of his girlfriend, Gabby Petito. He returned home from a cross country road trip without her and refused to speak with police, after which he vanished.

While social media Sherlocks peddled theories online about Mr Laundrie's location, the North Port Police - and later the FBI - have remained focused on their search of the T Mabry Carlton, Jr Memorial Reserve, a vast swampland just north of Mr Laundrie's home in North Port, Florida.

According to Mr Laundrie's parents, he frequently hiked in the reserve and spent a good deal of his time on the trails in the protected forests and swamps within. On September 17, six days after Ms Petito was reported missing, Chris and Roberta Laundrie - Brian's parents - reported him missing.

Initially they claimed he left home on 14 September to go hiking in the Carlton Preserve. It was later revealed that Mr Laundrie actually left home on 13 September. North Port police found Mr Laundrie's silver Mustang parked at the preserve, and have been searching for him in the swamps ever since.

The Carlton Reserve is a difficult place to search. It comprises more than 24,500 acres, most of which is inhospitable swamplands that frequently flood. Alligators, venomous snakes, and other varied creatures inhabit the nature preserve, which North Port police claim is "75 per cent under water."

The reserve also abuts the Myakka River State Park. A 12-mile trail within the reserve leads directly into the park, which sites to the reserve's north, meaning Mr Laundrie - if he is in the area at all - could be anywhere within the vast borders of the natural area.

Despite various reports placing Mr Laundrie on the Appalachian Trail, in Alabama, Ohio, Tennessee, and North Carolina, Mr Laundrie's parents believe the "only place" he may be hiding out is within the Carlton Reserve.

The family's lawyer, Steven Bertolino, told CNN they have no other guesses as to his location.

"They don't believe he's in another area," he said. "They believe he is in the preserve."

The current search in the preserve is being helmed by the FBI, and it appears they share they have taken the Laundrie's suggestions to heart. Since the day Mr Laundrie went missing, police have scoured the swamps searching for any signs of the man.

For more than two weeks there were no discoveries - at least none that were released to the public - despite police searching the area using airboats, swamp buggies, divers, drones and dog teams.

By late last week, the search at the Carlton Preserve had been scaled back, with only a small police presence left combing the swamp. On Wednesday, however, police activity surged at the reserve, with numerous law enforcement teams searching the area, including the Sarasota County Sheriff's Office. A fresh campsite was found in the reserve, which may have been built by Mr Laundrie.

Later Wednesday night it was revealed that Mr Laundrie's father, Chris, had been asked by law enforcement to join them in the search of Wednesday, but he was unable to do so. Instead, he joined law enforcement on Thursday morning, driving to the preserve around 10.30am, where he was driven into the interior of the swamp.

The elder Laundrie left the preserve just before 2.00pm.

FBI updates on the search for Mr Laundrie have become nearly non-existent since mid September, so the details of the elder Laundrie's involvement may not be known to the public for some time.