Daniela Green, who joined the top agency in 2011 and was granted a top-secret security clearance for work at its Detroit bureau, married the target of her investigation Denis Cuspert also known as Abu Talha al-Almani.
Cuspert, a German rapper turned ISIS pitchman was on the radar of counter-terrorism authorities for his growing influence as an online recruiter for violent jihadists.
According to report, the 38-year-old woman translator lied to the FBI about where she was going before travelling to Syria. She also warned her new husband he was under investigation.
Within weeks of marrying the operative, Greene realized her 'terrible' mistake and fled back to the US. On her return, she admitted of being guilty to making false statements was sentenced to two years in prison. She was released last summer.
"Greene's saga, which has never been publicized, exposes an embarrassing breach of national security at the FBI—an agency that has made its mission rooting out ISIS sympathizers across the country," the channel said.
"It's a stunning embarrassment for the FBI, no doubt about it," John Kirby, a former State Department official, told CNN.
Greene told CNN that she was fearful of discussing the details of her case. "If I talk to you my family will be in danger," Greene said.
She was born in Czechoslovakia and moved to the United States after marrying a US soldier.
When Greene was working with FBI on the investigation, Cuspert appeared in a video declaring his allegiance to the terror outfit.
In June 2014, after filling in a foreign travel form – as required for all FBI employees when travelling abroad – saying she was going to Munich, Germany to see her family, Greene instead flew to Istanbul, Turkey and from there traveled to Syrian border.
Once there she married Individual A, as Cuspert is referred to in the court documents.
Later, she send emails to an unidentifued person in July regretting what she has done and described herself as weak. “I really made a mess of things this time,” she said.
After about a month in Syria, Greene somehow was able to leave the war-torn country and returned to the United States. She was arrested on August 8, 2014, the report said.