The Twitter page of Deven Black, a nationally-recognised school librarian. In just three years he became destitute, his behaviour growing more and more bizarre.

This was a suburban dad, a nationally recognised school librarian. In just three years, he had become destitute. He had derailed his career with an inappropriate encounter with a female student, had blown up his marriage by giving thousands of dollars to paramours online and had gotten involved in a bank fraud scheme for their sake.

Doctors diagnosed depression. Relatives and friends tried to help, confronting and struggling to get through to him, mystified by his behaviour and questioning whether depression fully explained it.

A year after his death at 62, renowned brain experts have confirmed that more than depression was at work. They recently presented his case as “the mayhem of a misdiagnosis ” of a rare disorder. His estranged wife had suspected it, but his doctors hadn’t pushed to test him, and at least one had concluded he didn’t have it.

“I’m just so angry that this happened to him,” says his sister, Loren Black. “And I really wish that we could have figured out how to protect him.” “He got sick, but Deven was a good person.”

In this September 21, 2013 photo provided by the BAM Education Awards, Deven Black holds his prize for top school librarian in the country at an awards ceremony in Washington, D.C. Picture: BAM Education Awards via APSource:AP

His career was at a high point in the fall of 2013 when he stepped up to the stage at a black-tie gathering in Washington to accept an award for school librarian of the year.

It was a vote of confidence for a smart but contrarian high-school dropout who hadn’t started teaching until his 50s.

The intellectually omnivorous, independent-minded eldest of four siblings, Black got into one of New York City’s powerhouse selective public high schools, ditched it as stifling, and threw himself into an alternative newspaper and political campaigns. When most of his peers were in college, he was a radio reporter on Cape Cod, doing stories that spotlighted the lives of the elderly and disabled.

After returning to New York for a radio job that fell through, he started bartending and then managed a popular British-themed pub for nearly two decades, building the business through offbeat promotions. But he also earned a college degree in education, an interest that crystallised into a career and two master’s degrees after the pub closed in 2001.

Fired up to make a difference and full of ideas about how to improve schools, he became a New York City public school special-ed teacher, turned around an outdated middle school library and built a reputation in education circles as an earnestly iconoclastic blogger, unafraid to tell a conference that students drop out because “school sucks.”

Black was still a bartender when he met Jill Rovitsky on a blind date, and they bonded over what she calls “a mutual appreciation of the absurd.” They marked their 30th anniversary in 2013. They had a son on his college dean’s list, a home in Nyack, a historic, artsy town on the Hudson River.

This May 1983 photo provided by Rick Muscoplat shows Jill and Deven Black at their wedding in St. Paul, Minnesota. In 2013 they marked their 30th anniversary, had a son in college, a home in Nyack. Picture: Rick Muscoplat via APSource:AP

But the seeds of Black’s decline were germinating.

Four months before the award ceremony, school investigators had recommended disciplining him after a student said he made her uncomfortable by telling her she looked sexy and sometimes putting his arm around her shoulder, records show.

He told investigators he had hugged students only when they initiated it and wouldn’t have used the word “sexy”; he told his wife he was just trying to get the slinkily dressed girl to cover up. He was suspended without pay for two months in 2014 and removed from his librarian job, assigned instead to a full- time pool of substitute teachers.

Feeling down as the investigation played out, he spent more and more time online, forging virtual relationships while withdrawing from real-world ones, according to friends, relatives and court records.

One day, his wife noticed a peculiar slip of paper on the living-room floor: a receipt for $US300 Black had sent to someone in Africa. He explained it was for surgery for a co-worker’s relative.

About a month later, his wife found dozens more receipts, showing he’d dispatched about $US10,000, mostly to Ghana and Nigeria. She worried it was blackmail. He said it was an investment.

She warned him he was being scammed. Friends urged him to cut off his online contacts. But he plunged deeper into a web of virtual romances, telling friends he’d be bringing as many as a half-dozen dates to social gatherings. It was “clearly delusional, but he believed it,” says his oldest friend, Martin Mosbacher.

This 1995 photo provided by Jill Rovitzky Black shows Deven Black with his son, Jonas, at their home in Nyack, New York. Picture: Jill Rovitzky Black via APSource:AP

Black was so broke by the fall of 2014 that his wife paid his first month’s rent and security deposit when he moved out.

He wasn’t just giving money away. At the behest of an online “girlfriend” he said invited him to start a cocoa business, Black deposited a series of fraudulent checks, withdrew more than $US146,000 in cash and gave most of it to her, court papers say.

By January 2015, Black was under arrest in a Bronx jail for his bank schemes. Loved ones hoped it would be a wake-up call. Yet his response was an oddly jaunty email about encountering interesting defendants and kind guards. “I got one hell of an education,” he wrote.

What was Black’s problem? Was it internet addiction? Psychopathic personality disorder? Nothing seemed to fit.

“I was wrestling with growing suspicions that there was something significantly, organically wrong with him,” his wife says.

A matter-of-fact Minnesotan who works at a medical-education company, she’s careful about jumping to conclusions. But she kept thinking about an unusual disorder she’d heard about through her job. And as she started reading up, her suspicions mushroomed.

The disease, frontotemporal dementia, often emerges in patients’ 50s or 60s and can scramble their personality and behaviour while leaving memory intact, at least for a time. “Behavioural variant” FTD patients can become uncharacteristically impulsive, behaving inappropriately and making bad financial or other decisions without seeming to grasp the impact.

While the disorder’s causes aren’t completely understood, some patients’ families carry a genetic mutation linked to both FTD and amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease. Black’s late mother and brother both had it.

This 1997 photo provided by Jill Rovitzky Black shows Deven Black in the backyard of their home. Picture: Jill Rovitzky Black via APSource:AP

A psychologist suggested in 2014 that Black consider a neurological assessment, but nothing came of it, his wife said. Later, she mentioned FTD to a therapist and forensic psychologist who saw him in connection with the fraud case. “Enough of the descriptions of the condition ring true that I think it’s worth consideration,” she wrote in a 2015 email to the therapist.

The forensic psychologist, who declined to comment, concluded in court papers that Black didn’t meet the criteria for an FTD diagnosis at the time but recommended continued monitoring.

Black had been diagnosed with depression while hospitalised as a psychiatric patient for a week in June 2015, according to court records. He’d been evicted over unpaid rent and was living in his SUV, and he’d soon be pleading guilty to conspiracy to commit bank fraud.

But what had tipped him into suicidal despondency, his sister says, was that one of his supposed online sweethearts didn’t show up from Ghana for a promised visit. “It turned my stomach,” she said. “And it also broke my heart.”

By the time Black went to his October 2015 sentencing, he was living in a homeless shelter — friends and relatives say they feared he’d bring his schemes into their homes if taken in. Reassigned from teaching to administrative work after his arrest, he was facing at least suspension because of his conviction. But he had a line on a room to rent, said he’d continue therapy and was sentenced to probation and community service.

“I am on my way back,” he told the court in a letter.

A police officer stands guard at the entrance to the Boulevard Residence, the homeless shelter in the East Harlem neighbourhood of New York where Deven Black was killed in January of 2016. Picture: Mary Altaffer/APSource:AP

He would never get there. On January 27, 2016, a security guard found Black bleeding on the floor, his throat slashed, in his room in an East Harlem shelter for men with mental health problems. His volatile, 21-year-old roommate, Anthony White, fled when the guard opened the room’s door, police said. White’s family said he wasn’t a killer, but he never answered the allegations himself. His decomposed body was found in the Hudson two months later.

The day after Black’s death, his wife called Dr. Brad Dickerson, a professional acquaintance who runs Massachusetts General Hospital’s FTD Unit. He quickly agreed to explore Black’s case.

“When there is a story as compelling as Deven Black’s, in connection with a family history of something that we understand to be linked, then you’ve almost got two smoking guns,” said Dickerson, who worked on the case with Columbia University neuropathologist Dr. Jean Paul Vonsattel.

Confirmation came in an image of chemically stained, microscopic brown specks that marked deposits of a protein linked to FTD and ALS on a bit of Black’s brain.

“It’s good to know that there’s some explanation behind his behaviour,” says Mosbacher, but “it doesn’t change the fact that here’s somebody you’ve known for 50 years, and he’s suddenly going mad.”

Mosbacher, who bailed Black out, regrets having blamed someone who was sicker than he knew. Another friend, Emily Feiner, a clinical social worker, is enraged at what she views as the failures of mental health professionals.

This undated image provided by the New York Police Department shows Anthony White, the volatile, 21-year-old roommate of Deven Black in an East Harlem shelter for men with mental health problems. Picture: NYPD via APSource:AP

Yet it’s not unusual for FTD to go undetected, at least in early stages. The disease affects only an estimated 50,000 to 100,000 or so people in the US, compared with a likely five million with Alzheimer’s disease. FTD can be diagnosed in living patients by psychological tests and brain scans, but symptoms are frequently misattributed to depression, bipolar disorder or just a midlife crisis, experts say.

While there are no specific treatments yet to slow or stop FTD’s progression, Black’s relatives and friends feel a diagnosis could have helped protect him from harm.

A dementia diagnosis can factor into appointing a legal guardian to handle someone’s finances and care, though the crux isn’t a disease but a person’s capacity, notes elder law lawyer David Cutner. Some FTD patients turn to assisted living or nursing facilities, though those decisions depend on availability, finances and other questions. The average patient lives about seven years after diagnosis.

It was a diagnosis Black did not live to hear.

He left behind a strangely apt memento of a life that unravelled, and of his loved ones’ quest to understand how this could happen. “If you expect simple answers to complicated questions,” his Twitter profile says, “you’re in the wrong place.”