DETROIT -- Love can make you do strange things. Court documents tell the story of an FBI translator who went rogue and married a terrorist who was part of the Islamic State of Iraq and Syria (ISIS).

Denis Cuspert -- also known as rapper Deso Dogg. AP

He's known in Syria by the name Abu Talha al-Almani. In his native Germany, he's known as Denis Cuspert or the rapper "Deso Dogg."

But in this country, he's Individual A -- a recruiter for ISIS.

Calls for more attacks -- which included threats against President Obama as well as a beheading -- were enough to prompt a federal investigation into Cuspert's activities.

Denis Cuspert -- also known as Abu Talha al-Almani. CBS News

FBI translator Daniela Greene from the Bureau's Detroit office was part of the team tracking Cuspert. She accessed three Skype accounts, but provided only two to the FBI; the third was hers alone.

Daniela Greene CNN

Six months later, on June 11, 2014 -- according to court documents -- Greene, who is a German speaker, told her bosses she was leaving for a vacation in Europe. But she really went to see Cuspert in Syria, where the two were married on June 27 of that year.

Peter Trumbore CBS News

Peter Trumbore, an associate professor at Oakland University and an expert on terror groups, says her stay with ISIS was remarkable given that Cuspert knew she worked for the FBI.

"I have not seen a similar case in counterterrorism context," Trumbore said.

We asked if she could have very easily wound up dead.

"Yeah, that would have been the expectation. That would be the thought," he said.

Especially because 11 days after her wedding, the bride was expressing serious doubts.

"I was weak …" Greene said in an e-mail to an unidentified person in the U.S. "I didn't know how to handle anything anymore. I really made a mess of things this time."

CBS News

Somehow, she escaped from ISIS in Syria, knowing she'd be arrested upon her return to the States on Aug. 6. She served two years in prison for lying to the FBI.

"There is some embarrassment there ... but the information she could potentially have brought back ... to be with senior members of the organization, that is really valuable information," Trumbore said.

To the best of the authorities' knowledge, Cuspert is still alive. While Greene was released from prison last summer, so far she's declined to speak publicly about her case.