Prosecutors granted immunity to an ex-girlfriend of Representative Matt Gaetz before she testified last week in front of a federal grand jury hearing evidence in the investigation of the congressman, according to a source familiar with the matter.

Gaetz has been under investigation to determine if he violated sex trafficking laws and obstructed justice in that probe. Gaetz has previously denied all wrongdoing, and has said he has never paid for sex nor had sex with an underage girl. 

The woman, who CBS News is not naming to protect her privacy, testified in front of a federal grand jury in Orlando last Wednesday. She is viewed as a potential key witness, according to two sources familiar with the investigation. One of the sources said she has information related to the investigation of both the sex trafficking and obstruction allegations.

“This may be a willing participant who has a smart lawyer who sought an immunity deal from the government,” said former prosecutor and CBS News legal analyst Rikki Kleiman. “The government does not give immunity blindly, they know what they’re getting in exchange.”

Isabelle Kirshner, an attorney for Gaetz, told CBS News in a statement last week that “we have seen no credible basis for a charge against Congressman Gaetz. We remain steadfast in our commitment to challenge any allegations with the facts and law.”

A source told CBS News last week that as a part of an obstruction probe, investigators are looking into whether Gaetz had a phone call with the ex-girlfriend, and another woman, who was already a witness in the federal investigation. 

Multiple sources told CBS News that the ex-girlfriend and the other woman traveled to the Bahamas with Gaetz in 2018, along with a third woman with whom Gaetz was in a sexual relationship. That third woman was 18 at the time of the Bahamas trip, but investigators are also looking into whether she was 17 when the sexual relationship began. 

Investigators are trying to determine if any of the women were paid and were illegally trafficked across state or international lines for the purpose of sex with the congressman. 

Two sources familiar with the matter told CBS News it was Joel Greenberg, a former Florida county tax collector and associate of Gaetz’s, who introduced Gaetz to that woman when she was 17 years old. Greenberg pleaded guilty in May 2021 to six federal charges, including trafficking of a minor.