The 62-year-old ex-teacher who was fatally stabbed to death by his roommate in an East Harlem homeless shelter was a "model citizen" before he succumbed to depression, eventually losing his career, wife, and home.

Deven Black, 62, was killed Wednesday night after shelter roommate Anthony White allegedly stabbed him in the neck during an altercation over a stolen cell phone. White, who is mentally ill, is still at large, and details about both men's lives have been filtering in in the wake of the stabbing.

Black was a former middle school Social Studies teacher and librarian, and before his life unraveled, he lived in Nyack, NY with his wife and now-college aged son. He was involved in the community, serving as president of the Parent-Teachers Association at Upper Nyack Elementary School and reviewing restaurants for The Journal News. But in 2013, Black began struggling with depression—he started sending money to people he met online, lost his job after he allegedly told a 13-year-old she looked "sexy" and touched her inappropriately, and got divorced from wife Jill Rovitzky. In 2014, he began depositing fraudulent checks for a woman he met online, and pleaded guilty in federal court to bank fraud

"I am so deeply ashamed of what I have done," Black wrote in a letter to the judge in his case. "Not only have I committed bank fraud, I have thrown away 60 years of law abiding productive life (...) In many ways, I was a model citizen. I have tossed all of that away in a perfect storm of extreme loneliness, depression and greed."

Friends and family members suspected he suffered from more than depression, but he was not appropriately treated. "He was never properly diagnosed,” Emily Feiner, a clinical social worker and family friend, told the Times. "He was compulsive and had almost delusional thought patterns that influenced his choices." When he became homeless, he was unable to get prescription medication to help manage his mental health issues.

White, who is only 21, has similarly suffered from mental health problems, briefly spending time in a facility in 2013. He was never considered violent, though residents told reporters he'd been making death threats in the week leading up to Wednesday's attack. Mayor de Blasio says the city will increase security in 27 shelters and hire medical staffers who can help residents with mental illnesses.

“I send my condolences to the Black family, I really do,” LaSandra White, White’s sister, told the Times. “But this is a problem in the system. How did this happen? How did a weapon even get inside? This is supposed to be a mental health shelter. The system is failing our community. It’s failing people with mental illnesses.”