Scuba diver who disappeared during or after a cave dive
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 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. 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). A reward they offered was rescinded in 2012 after the death of another diver who may have been trying to collect it, vindicating the criticism of the divers who had warned of that possibility and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 that his 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" was 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 McDaniel 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.
Background.
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. He 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 had not been prescribed opiates.
His parents 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. He accepted the offer and moved into the house in April 2010. His parents and girlfriend say the move was proving beneficial, as McDaniel was beginning to think and talk about moving on from his recent personal setbacks.
Relocating to the Gulf Coast allowed McDaniel 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.
Vortex Spring.
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 fed by the Floridan Aquifer. Diving instruction is offered for all levels; experienced divers come for the underwater wildlife and the cavern, which begins 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, the main attraction of Vortex Spring is the cave, which starts from the cavern, at a depth of . At the entrance is a sign depicting the Grim Reaper which warns divers of the dangers of continuing onward. The cave steadily narrows, reaching a makeshift rebar gate with a chain and padlock, at a point almost 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. 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. Beginning at the gate, over through the area's limestone bedrock have been mapped, to a depth of ; the cave's full extent is unknown. At some points, the passage narrows to , 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 McDaniel during trips to Vortex Spring. (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. "Ben was fearless. He followed his passions."
Disappearance.
In mid-August, four months into his Florida sojourn, McDaniel returned to Tennessee for a week. His parents and girlfriend, Emily Greer, said he seemed optimistic. He told them he was working on getting certified as an instructor so he could find a job and that he was researching cave diving with an eye toward getting that certification as well. On his nights out with Greer, he told her of plans to eventually start a diving-related business. On the weekend of August 14–15, he returned to Florida, leaving behind a letter thanking his parents for the sabbatical and promising to look after them as they grew older. They never saw him again.
On August 18, the Wednesday after he returned to the Santa Rosa Beach house, he went up to Vortex Spring again. In the middle of the day, he did one dive. Other divers saw him looking closely at the area around the cave entrance as if he was planning something. After resurfacing, he was recorded on security cameras making a transaction to fill his tanks at the dive shop. He spent much of the rest of the afternoon by himself alongside the spring, witnesses said, testing equipment and making notes in his dive log.
The day had been hot, with temperatures around , and as evening came McDaniel began preparing for another dive. He called his mother on his cell phone, the last contact he had with his family. Around 7:30 p.m., as the sun began to set, he went in again.
Cronin and fellow employee Eduardo Taran, on their way back from a dive themselves – something they often did on Wednesdays after the shop closed – saw McDaniel as he began descending, with his lights on and wearing a helmet, suggesting he was venturing into the cave. Taran, who had suspected for some time that Ben was forcing the gate open, went down to him and unlocked it, watching McDaniel go in and then returning to Cronin. No one is known to have seen him since.
On some nights when they had seen McDaniel dive late, the two had stayed at the spring after resurfacing until they saw bubbles on the surface, indicating that he was beginning to decompress in order to safely resurface. On the night of the 18th, they instead went back to Taran's house for coffee.
McDaniel's truck was still in the parking lot the next morning, but with many summer visitors coming to enjoy the site's many water-based recreational opportunities and picnic grounds in addition to diving, the employees said they were too busy to notice. They did see the truck the next morning. After determining that no one else had seen McDaniel, Taran called the Holmes County sheriff's office.
Search.
Upon arrival, the sheriff's deputies sealed off the spring with crime-scene tape. McDaniel's tanks, wet suit and other diving equipment were not present and there were no signs of a struggle near his truck or anywhere else he could have been. His wallet, with almost $1,100 in cash, and cell phone were in the cab of his truck; dive logs showed that he had explored the cave and a map he made was also found. 
At the Santa Rosa Beach house officers found his dog, hungry from having been unfed for two days. Based on these circumstances, police and dive shop employees assumed that he had never resurfaced and had in all probability drowned somewhere in the cave trying to get out. Cadaver dogs alerted on the water surface, further supporting that theory.
Reports of a missing diver in the Vortex Spring cave spread and other cave divers volunteered for what they assumed would be a recovery operation, taking advantage of the weekend. McDaniel's parents were called, and they drove to Florida, along with Greer, to observe from the shore. News media in the Panhandle and Memphis followed the search closely.
Captain Harry Hamilton, an investigator in Holmes County, assumed at first that a very large number of divers, both amateur and expert, would volunteer to search for and recover McDaniel's body. He soon realized that very few divers "in the world" possessed the training and skill to attempt such a dangerous cave diving recovery. Experienced divers scoured the cave, investigating small crevices and fissures McDaniel might have entered in a panicked attempt to exit the cave as his tanks ran low, which was a pattern found in other cave diving deaths. It was risky work, and one diver said they had nearly died during the search. Multiple divers searched through the weekend, but did not find McDaniel.
Discovery of tanks.
Two tanks known to belong to McDaniel were found near the entrance to the cave. This discovery struck some searchers as inconsistent with McDaniel's supposed intent to explore the cave, as cave divers usually place extra "air" tanks for decompression at points along their exit route, and not only at the entrance to the cave. When tested, the tanks were found to contain normal air and not the specialized gas mix required for diving at depth. McDaniel would have been aware of