Ben McDaniel

Beginning at the gate, over 1600 ft through the area's limestone bedrock have been mapped, to a depth of 310 ft; the cave's full extent is unknown.

At some points, the passage narrows to 10 in, requiring divers to remove their tanks, push them forward through the passage, and then twist their bodies to follow.

McDaniel's dives at the site were regular enough that the dive shop employees and other frequent visitors came to know him.

One of the employees, Chuck Cronin, believed that while McDaniel had the proper equipment and considerable diving knowledge, he was often overly confident in his abilities and not shy about saying so.

That opinion, the Memphis Commercial Appeal later reported, was shared by posters on a scuba diving website, scubaboard.com, who had also met Ben during trips to Vortex Spring.

This policy was instituted after the deaths of 13 divers in the cave during the 1990s, and in response to threats from the state to ban diving in the cave entirely.

In the late 2000s Ben McDaniel was going through a difficult period in his life.

The oldest of three sons born to Shelby and Patty McDaniel, a wealthy couple who lived in Collierville, Tennessee, outside Memphis, he had returned to live with his parents after his marriage ended in divorce and his construction business failed, the latter leaving him with tax debts of almost $50,000 to the Internal Revenue Service and the state of Tennessee.

He was also still grieving for his younger brother Paul, a frequent rock climbing partner during their youth, who died in 2008 at the age of 22 from a stroke.

Ben had found Paul unconscious in the family home and tried to revive him; he later became active in raising money for the foundation his parents established to support research into prevention and treatment of strokes.

Later, it was revealed that Paul's cause of death was "anoxic encephalopathy due to combined drug (opiate/benzodiazepine) toxicity", a drug overdose, not a stroke.

Paul was not being prescribed opiates.

The McDaniels suggested their son take a sabbatical, offering to support him financially while he and his dog, a chocolate Labrador he had rescued, lived in the family's beach home at Santa Rosa Beach on the Emerald Coast of the Florida Panhandle.

On August 20, 2010, Ben McDaniel (born April 15, 1980), of Memphis, Tennessee, United States, was reported missing after employees in the dive shop at Vortex Spring, north of Ponce de Leon, Florida, noticed that his pickup truck had remained in the shop's parking lot for the previous two days.

McDaniel, who had been diving regularly at the spring while living in his parents' nearby beach house, had last been seen by two of those employees on the evening of August 18, on a dive entering a cave 58 ft below the water's surface.

While he was initially believed to have drowned on that dive, and his parents still strongly believe his body is in an inaccessible reach of the extensive cave system, no trace of him has ever been found.

He accepted the offer and moved into the house in April 2010.

His parents and girlfriend say the move was proving beneficial, as Ben was beginning to think and talk about moving on from his recent personal setbacks.

Relocating to the Gulf Coast allowed Ben to indulge in his preferred hobby, scuba diving.

He had first taken it up at the age of 15, practicing with his tanks in the family pool.

Despite living on the coast during his sabbatical, he preferred to dive in fresh water, becoming a frequent visitor to Vortex Spring, located inland a short distance north of Ponce de Leon.

At Vortex Spring, which claims on its website to be the largest diving facility in the state, divers descend into clear waters at a constant temperature of 68 F fed by the Floridan Aquifer.

Diving instruction is offered for all levels; experienced divers come for the underwater wildlife and the cavern, which begins 58 ft below the surface.

All divers are required to present proof of open-water certification and sign a release of liability.

For the most experienced divers, some of whom come from around the world, the main attraction of Vortex Spring is the cave, which starts 300 ft from the cavern, at a depth of 115 ft. At the entrance is a sign depicting the Grim Reaper which warns divers of the dangers of continuing onwards.

The cave steadily narrows, reaching a makeshift rebar gate with a chain and padlock, at a point almost 300 ft from the entrance.

The dive shop withheld the gate key, unless a diver showed proof of cave diving certification, which requires two months' training including 125 dives with an instructor or certified diving partner.

A reward they offered was rescinded in 2012 after the death of another diver who may have been trying to collect it, vindicating the criticism of the divers who had warned of that possibility and resented the McDaniels' insinuation that those who had searched for their son at great personal risk had not been "brave" enough.

Although the McDaniels continue to believe Ben's body is in an area of the cave beyond the reach of current search capabilities, they have also entertained the possibility that his death was not an accident but the result of foul play.

A private investigator they hired believes that his body may have been removed before any authorities were contacted, or that he may even have been murdered on land and the narrative of his disappearance fabricated as a cover story.

A segment of Investigation Discovery's Disappeared has been devoted to the case, as well as Ben's Vortex, a documentary co-directed by diver Jill Heinerth.

In addition to the accident and murder theories, the documentary also considers the possibility that Ben staged the disappearance to escape a troubled recent past that included a divorce and financial setbacks.

The McDaniels have vehemently rejected that theory, pointing to the dog and girlfriend he left behind as well as doubting that he would have knowingly subjected them to that level of grief after seeing how his brother's death had affected them.

The state of Florida issued his family a death certificate in 2013.

McDaniel had been living at his parents' beach house on the Emerald Coast during a sabbatical in the wake of a divorce, a business failure, and the death of his younger brother two years earlier.

An avid diver since his teens, he had been a regular at the spring, where he had apparently been covertly exploring the cave despite lacking the required certification.

Lengthy searches have only located some anomalously placed and filled decompression tanks; many of the divers who took part in those searches believe that if McDaniel is indeed dead, his body is not in the cave as he was too large to enter its narrower passages.

The McDaniels devoted their family's extensive financial resources to the search, at one point guaranteeing the replacement cost of a remotely operated underwater vehicle (ROV).

(According to a 2014 online comment by his father, he could not find anyone at Vortex Spring willing to be his diving partner, so he did his dives alone.) His parents later defended him from those criticisms by seeing them as positive traits.

"Ben was brave," his father later said.