One month before former FBI agent and purported CIA freelancer Robert Levison disappeared off Iran's Kish Island in 2007, a high-level Iranian defense official disappeared in Turkey.

The first disappearance was a kidnapping. The second, reports say, was a defection. More than a decade later, the two may be inextricably linked.

A new investigation by Reuters alleges that prior to the controversial Iranian prisoner swap deal in 2015, U.S. officials pressed Iran to either turn over or at least provide conclusive information on the whereabouts and condition of the former FBI agent. Photos previously released by Levinson's captors suggested he was being held by an unknown criminal or extremist group, but U.S. officials long-suspected that Iran was holding him or at least knew where he was.

In response to the Levinson request, the Iranians made a "startling offer," Reuters reports.

"In return for Tehran's assistance in recovering Levinson, they wanted Washington to reveal the location of Ali Reza Asgari, an Iranian general..." Reuters reported. (In 2017 The New York Times also noted Iran's interest in Asgari during talks related to Levinson.)

So who's Asgari?

According to published reports, Asgari was a high-level defense official who served for decades in the Iranian military, including its infamous Revolutionary Guard, and eventually made it all the way up to deputy defense minister. The German magazine Der Spiegel reported that in 2005 Asgari had fallen out of favor with the newly elected Iranian president, Mahmoud Ahmadinejad, and fled the country with the help of the CIA. (Some Iranian officials and Asgari's family reportedly suggested it was not a defection, but an abduction.)

Either way, the American and Israeli debriefers "soon discovered that the Tehran insider was an intelligence goldmine," Spiegel reported. Asgari purportedly revealed critical new information about the scope of Iran's nuclear program.

The intelligence reportedly won Asgari a ticket to Germany and then to the U.S., "somewhere in Texas."

A book published in 2014 and allegedly based on interviews with dozens of current and former intelligence officials claimed that Asgari had been granted asylum in the U.S. At the time the CIA declined to comment on the case and, in its new report, Reuters said the CIA told other U.S. officials during the negotiations that it didn't know where Asgari was.

Without Asgari to trade, the deal for Levinson died.

"It became pretty clear pretty soon that this was not something [the Iranians] were prepared to budge on," Reuters quoted a former U.S. negotiator as saying.

In January 2016 five Americans were freed from Iranian custody and sent home, in exchange for seven Iranians who were serving time or awaiting trial in the U.S. Robert Levinson was not one of the Americans freed.

Read More: Robert Levinson, The American 'Left Behind' in the Iran Prisoner Swap (ABC News)

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