“By now they might know me,” Derek Abbott said, glancing around the Somerton cemetery for the groundskeepers. On December 1, 2014, 66 years to the day after the Somerton Man’s demise, Abbott, a physicist and engineer at the University of Adelaide, was taking me to his grave. For years, someone had placed flowers on it; some said it was the nurse. The original letters on the gravestone had become loose, and a few had fallen on the ground. We picked through the pebbles in the blazing sun, finding chunks of alphabet that we plugged back into the small headstone until it read: Here lies the unknown man who was found at Somerton Beach 1st Dec. 1948 .

Of all the amateur detectives who have dedicated themselves to the mystery — including a postman in New South Wales who has claimed the Somerton Man was a Russian spy, another man who thinks he is the American big-band leader Glenn Miller, and a number of internet oddballs who specialize in magnifying the letters of the code and seeing micro-writing that isn’t really there — Abbott is the most devoted. He has become a celebrity among followers of the case — his Reddit “Ask Me Anything” last year yielded nearly 500 questions and answers — and sees his role partly as keeping wilder speculation in check. “As a scientist, you’re taught to be dispassionate,” he told me. “You’re not supposed to get crazy when your pet theory turns out to be unlikely.”

But some of Abbott’s fellow investigators think his obsessions and celebrity have led him astray and turned him into a Pied Piper of true-crime nerds. “Abbott is like a dog with a bone,” says Gerry Feltus, a retired Adelaide homicide detective who is his main rival. “If he weren’t such an educated man, he’d make an excellent busker.”

Derek Abbott at the Somerton Man’s grave

Abbott, 55 years old and with thinning dark hair, is gainfully employed, although over several days in Adelaide, his free time to discuss this case appeared almost limitless. He drove me around in his SUV , which had multiple child car seats fastened in the back for his three young children. (He also has two grown daughters and a son from a prior marriage.) Obsessions tend to find Abbott. He has, by his own account, been happily consumed by them since he was a child in London. Many were scientific: At the age of 10, he says, he requested a copy of the British Pharmacopoeia, a technical manual of pharmacology. At 15, he began traveling all over London and researching the history of old lampposts and letter boxes. His demeanor is distinctly professorial, though not in an absent-minded way. He talks slowly, with an engineer’s precision, and favors nice suits over tattered tweed, even in the Australian summer heat.

“It’s a bit like Phoenix,” Abbott said, a little apologetically, as we drove through his city. When the beach isn’t in sight, the comparison feels about right: Adelaide and its environs are mostly flat and arid, with the suburbs giving way to desert. Even its urban grid recalls the American Sun Belt, with orderly streets characteristic of a place whose city fathers left nothing to chance. Unlike other areas of Australia, Adelaide was settled exclusively by free British colonists, not by convicts. When planning the city in 1837, its founders didn’t bother to set aside space or resources for a jail, reasoning that it wouldn’t be necessary for a population of honorable women and men.

But to understand the So­­merton Man case, Abbott told me, “you do have to know that Adelaide has a reputation for these things.” Ruth Balint, an Australian cultural historian, put it more bluntly: “It’s a city of churches and of weird, sick murders.” When Salman Rushdie visited Adelaide in 1984, he called it “the ideal setting for a Stephen King novel, or horror film.”

The man carried an Army Club cigarette pack, but the brand inside was Kensitas.

Adelaide’s homicide rate isn’t abnormally high, but what it lacks in volume it more than compensates for in creepiness. The city has become known as Australia’s “murder capital,” the site of a string of gruesome serial killings and mysterious disappearances. In 1966, three young siblings disappeared and were presumed kidnapped after a trip to Glenelg Beach, near Somerton; they were never found. In the 1970s and 1980s, a shadowy group of upstanding, professional citizens of Adelaide, known as the Family, drugged, sexually abused, and murdered young men; those crimes were never fully solved either. Last year, police in South Australia announced $13 million in reward money for information about the murders or disappearances of 18 children between 1966 and 2000.

In 2003, during the investigation of another grisly set of killings known as the Snowtown or “bodies-in-­barrels” murders, local detectives approached Abbott and asked him to examine the unusual characteristics of one of the 12 victims’ hair. The detectives had found tiny ­bubble-shaped articulations at the tips, and they wanted an electrical engineer to determine whether the deceased had been electrocuted. “I tried electrocuting samples of my own hair,” Abbott said, “and I found that the only thing that would do that is heat.” The body had been cooked, not electrocuted.

Thrilled by his small contribution to the prosecution’s case, Abbott remembered an article he’d read about the Somerton mystery in 1995, in a magazine he picked up at a laundromat. “There’s something in this that stuck in my mind — something haunting,” he said. He was, in part, troubled by the inconsistencies and contradictions. “There were so many loose ends. And there was something sad about it — something desolate about a man dying alone,” without anyone to mourn him or even to confirm that he ever lived.

Abbott’s desk, with documents related to the case

In 2007, Abbott began investigating the case. He eventually turned to Facebook and like-minded obsessives around the world to track down facts that in previous eras might have taken Holmesian knowledge or resourcefulness. Take the necktie. The direction of the stripes turns out to be significant because Commonwealth tie makers and American tie makers slanted their stripes in different directions: The Somerton Man wore an American tie, a rarity in Australia at the time. Other clues have led Abbott to look up, say, the record-keeping habits of laundry services in mid-size Australian cities in 1948 or the price of various tobacco brands. Sometimes this information yields faint clues to the Somerton Man’s story. Most often it reveals how far from the truth Abbott remains and produces only more questions. Someone suggested that the Rubáiyát was a book cipher — a spy codebook — setting in motion an eerily difficult quest to find an identical copy and test it against the code. (The cops threw away the original at some point during the 1950s.) No identical copy could be found. It appeared that the Somerton Man’s Rubáiyát was unique and published by a company in the habit of issuing, for obscure reasons, one Rubáiyát at a time.

The labels of the man’s clothing were torn out.

On the hunch that the Rubáiyát was being used as a book cipher, Facebook group members combed Australian newspapers for stories about other men who died unnaturally, accompanied by a Rubáiyát. Incredibly, they found one, an immigrant named George Marshall who poisoned himself with barbiturates and died with a Rubáiyát next to him in Sydney. It was not the same edition as the Somerton version. Instead, it was identified as a seventh edition published by Methuen, a London-based press. The interest would have ended there if Abbott hadn’t tried to find a Methuen seventh edition of the Rubáiyát and discovered that the company never published any edition beyond the fifth.

Abbott’s code-breaking efforts, for which he initially held high hopes, stagnated. He tried to solve the code by treating it as a substitution cipher, in which every letter stands for another. He has tested that theory with computational models and conclusively ruled it out. He tried to determine if the letters were random, and even at one point had his students drink beer and write down random letters in progressive stages of inebriation to see if the letters resembled the patterns of those in the code. They did not.

So far, he has excluded, with mathematical certainty, a whole range of standard code types — 40 types of known cipher. Recently he’s been testing another theory, first put forward by Navy cryptographers in 1949. The frequency of occurrence of letters on the Rubáiyát’s back cover fits unusually well the frequency of occurrence of the initial letters of English words. Abbott now thinks that the code is not a code at all, but a series of letters someone — perhaps the Somerton Man — wrote in order to commit something to memory. The first five letters — WRGOA — could, on this hypothesis, have just been a reminder to buy watermelon, rice, grapes, oats, and artichokes. Abbott tested the initial-letter hypothesis against samples of text from more than 30 languages, and English repeatedly surfaced as the best statistical fit. But of course, to know what the letters stood for, we’d have to ask their author.