In early March, a small group of private investigators, including two former FBI agents, gathered for a meal at Old Tbilisi Garden, a restaurant in Greenwich Village that specializes in Georgian food.

It was a somber occasion. Two months earlier, the United States and Iran had exchanged prisoners, including several Americans held in Tehran's notorious Evin Prison. Another American, Robert Levinson, long missing in Iran and a friend of those present, was not part of the deal. Levinson, a former FBI agent who became a private investigator, also had another life: as a consultant for the CIA.

In March 2007, Levinson, then 59, disappeared on Kish Island, in the Persian Gulf off the coast of Iran, while trying to recruit a fugitive U.S.-born assassin as a CIA source inside Iran. He was last seen alive in 2010 in a hostage video pleading for help and in photographs wearing a Guantanamo-style jumpsuit. The images did not disclose who was holding him. It is not known whether Levinson, who was eager to expand his role at the CIA and who apparently decided on his own to go to Iran, is still alive.

The event at Old Tbilisi was held to observe the ninth anniversary of his disappearance. Former colleagues toasted him and traded stories. Levinson, like those present, had spent his career in a shadow land, one where spies, agents and private eyes persuade informants to spill secrets in exchange for money or a deal. It is a risky game that can pay off big or that can go very wrong, as Levinson's trip to Iran did.

The two former FBI agents at the dinner, Joseph O'Brien and Andris Kurins, were familiar with that terrain.

The former agents had tried to help the FBI find their missing friend. O'Brien recruited a former Iranian army general to go to Tehran to seek out information. But as with other investigators who knew Levinson, their offers were rebuffed by the FBI.

"I was told, 'Why don't you mind your business?' " recalled Kurins.

Levinson and his wife, Christine, lived for years in Coral Springs and raised their seven children there, but he was a New Yorker in every other way. He grew up on Long Island, attended City College, and worked in New York on celebrated cases both as an FBI agent and as a private investigator.

From the start of his career, Levinson saw himself as a collector of informants, someone skilled in extracting information from people eager to catch a break from the law or in need of a favor, like a U.S. visa. By the late 1970s, he had his dream job, working in the FBI's New York office, helping to coordinate intelligence about the Mafia gathered by agents in the metropolitan area.

O'Brien, who also wanted to investigate the mob, knew he had found his mentor when he first met with Levinson. His office, O'Brien recalled, was lined with photos of gangsters and charts showing the hierarchies of New York's major crime families. "He was a master, and he taught me a lot," O'Brien said.

In 1983, the two men shared an FBI achievement award. But Levinson's FBI career nearly ended over his handling of an informant in another big Mafia case.

His source was a onetime schoolteacher named Michael Orlando, who had turned to robbery. When faced with the prospect of more jail time, he agreed to cooperate with the FBI as a paid informant on another local crime family, the Genoveses.

Levinson believed that Orlando was critical to building a sweeping case that would result in indictments against politicians, labor leaders and police officers. But some bureau officials suspected that the FBI agent had fallen into the classic informant's trap, with Orlando feeding him tidbits of information while using his protected status to carry out crimes.

Levinson and other agents fought to keep using Orlando. But when FBI supervisors decided to arrest him and end the investigation, a bitter dispute broke out inside the FBI that cost Levinson his position in New York and led to his decision to move to Florida.

There, he became an expert in the FBI's Miami office on Colombian drug cartels and Russian organized crime. After his retirement in 1998, he took a familiar path, followed by many former agents, into the private sector, working for corporate investigation firms and setting up his own one-man shop.

Investigators like Kurins said they did not believe the story that the U.S. government had put out to explain why Levinson was in Iran — that he had gone there to track counterfeit cigarettes.

"It was impossible that he would go to Kish Island on a cigarette case," Kurins said.

Several months after Levinson's disappearance, another of his acquaintances in New York, John Moscow, a lawyer, checked his email and found what appeared to be a clue. Moscow, a former top prosecutor in the Manhattan District Attorney's Office, was one of several people copied on an email in which Levinson, or someone pretending to be him, pleaded for help from U.S. officials.

Moscow said he had turned the email over to the FBI, adding that he had never heard back.

FBI officials told Levinson's family that they thought the email was a fake. But three years later, when an email arrived containing a video showing him as a hostage, it seemed that the bureau may have made a mistake. The 2007 email received by Moscow and the 2010 message with the video were sent from Gmail accounts bearing nearly identical names, according to a new book about Levinson and the search for him, Missing Man: The American Spy Who Vanished in Iran.

A spokeswoman for the FBI declined to comment.

The Obama administration has said it is committed to finding Levinson.