(CNN) — The Justice Department is investigating potential obstruction of justice connected to the ongoing probe of Rep. Matt Gaetz and his alleged sexual relationship with a minor.

According to two people familiar with the matter, federal investigators’ concerns over efforts to obstruct the probe date back to at least last fall, when the examination of the Florida Republican was not yet public knowledge.

One of the people said investigators have been told about Gaetz and an associate discussing a plan to talk with Gaetz’s ex-girlfriend in October 2020 about the ongoing sex crimes investigation. Investigators have also been provided material about the alleged discussion, the person said.

Politico first reported the obstruction investigation on Wednesday night with additional details about what is being scrutinized. According to the outlet, investigators are also looking specifically at a phone call that Gaetz had with a witness in the sex crimes investigation. The phone call had originated between the witness and Gaetz’s ex-girlfriend, and at some point during the conversation, the ex-girlfriend patched Gaetz into the call, the outlet reported.

Politico did not report when the call took place and noted that it was unclear what was said between Gaetz and the witness on the call.

Gaetz’s ex-girlfriend, a former Capitol Hill intern, is seen as a critical witness, as she has been linked to Gaetz as far back as the summer of 2017. That period of time has emerged as a key window of scrutiny for investigators in part because that is when Gaetz is accused of having sexual contact with another woman who was 17 years old at the time.

Last month, CNN reported that federal authorities had secured the ex-girlfriend’s cooperation in the probe but the sources who spoke to CNN at the time would not say if she had entered into a formal cooperation agreement. A person familiar with the matter said Wednesday that she had not yet spoken to investigators and a formal agreement was still not in place.

The obstruction of justice investigation heightens the legal jeopardy that the congressman could face. If authorities believe that Gaetz or his associates attempted to influence someone’s testimony to investigators, they could be charged with witness tampering, a federal crime that could result in prison time.

Gaetz has long denied having sex with a 17-year-old and has not been charged with any wrongdoing.

“Congressman Gaetz pursues justice, he doesn’t obstruct it,” Gaetz spokesman Harlan Hill said in a statement. “After two months, there is still not a single on-record accusation of misconduct, and now the ‘story’ is changing yet again.”

The associate who one source had said discussed with Gaetz a plan to speak with the ex-girlfriend said he did not believe the discussion between Gaetz and himself had happened.

The Justice Department referenced an obstruction investigation in a subpoena sent to an associate of Gaetz’s in late December, according to the associate.

The Justice Department first began scrutinizing Gaetz in the final months of the Trump administration, officials have said, as part of a separate sex-trafficking investigation into his friend, a former county tax commissioner named Joel Greenberg.

Greenberg entered into a plea deal with prosecutors last month where he admitted to six federal charges, including that he knowingly solicited and paid the 17-year-old for sex. He remains in jail as he awaits his sentencing.

Greenberg was never charged with obstructing justice, but in his plea agreement he admitted to contacting the 17-year-old after learning in 2020 that his sexual relationship with her was under investigation and asking her “for help in making sure that their stories would line up, because he knew that his commercial sex acts with her were illegal.”

Greenberg also contacted the 17-year-old directly and through one of her friends “for the purpose of asking (the 17-year-old) to lie” about the reason he had looked her up in a Florida driver’s registration database in 2017 when “he had reason to believe that the (17-year-old) was under the age of 18,” according to the plea agreement.

It’s not clear exactly when Gaetz learned he was under investigation but a person familiar with the matter said that he hired a Florida criminal defense attorney last year. He has since bolstered his legal team with two high-powered attorneys based in New York.

In August, according to text messages first reported by Politico and later confirmed to CNN by a person familiar with them, Greenberg wrote that he was warning men who had come in contact with the young women of the FBI’s interest.

The investigation into Gaetz did not become public knowledge until a report in The New York Times in March, and in the preceding months, the outspoken Republican did not betray a hint of the legal troubles he was battling.

But investigators are now examining if Gaetz or any of his associates did anything to attempt to interfere with the investigation, according to the sources, including whether he and an associate visited the ex-girlfriend, who worked at the time for a state agency in Tallahassee.

She has since resigned from the position effective July 1, according to a spokeswoman for the agency. Her lawyer, Tim Jansen, confirmed to CNN that she had submitted her resignation but said that “her departure has nothing to do with the ongoing investigation.”

The ex-girlfriend’s cooperation with the government is seen as critical because of her proximity to Gaetz in 2017.

Investigators also believe she can help them understand the relevance of hundreds of transactions they have obtained records of, including those involving alleged payments for sex, people familiar with the matter said.

In April, Politico reported that the ex-girlfriend was concerned that she could face obstruction charges after talking on the phone with the alleged 17-year-old victim and her roommate. The ex-girlfriend was friends with the women and suspected they could be recording the call, the outlet reported.

The months-long examination into questions of whether Gaetz was involved with a minor has so far drawn in a cast of young women who were friends with each other and partied with the congressman and other influential Republicans.

Investigators have sought interviews with several of the women, including the alleged underage victim and Gaetz’s ex-girlfriend. Information that some of them have provided is among the evidence being reviewed by the Justice Department as officials seek to determine whether the congressman should be charged.

Spokespeople for the Justice Department and the FBI declined to comment for this story.

Since the allegations against him became public, Gaetz has remained defiant and accused the Justice Department of targeting him because of his politics.

Gaetz’s defense team has also quietly sought to gauge the support of some of the women he partied with as well as other people in his circle who are of interest to investigators.

According to text messages reviewed by CNN, a private investigator who said they worked for Gaetz’s defense team began reaching out in April to one woman who had been previously connected to Gaetz.

The woman did not engage with the private investigator, according to her friend, but had been told that the private investigator had spoken with at least one other woman involved in the case.

Around the same time, Gaetz’s lawyers contacted an attorney for another person under scrutiny in the investigation to ask about that person’s involvement with a grand jury hearing evidence about the case, according to a person familiar with the matter.

Such outreach is not uncommon or illegal, although it could cross into witness intimidation if “there is some message communicated that’s either a carrot or a stick,” said Elie Honig, a former prosecutor and CNN senior legal analyst.

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