The legal firestorm around Rep. Matt Gaetz is heating up. Here are 13 key people to watch.

• Rep. Matt Gaetz's ex-girlfriend testified before a federal grand jury in early January.

• Authorities have already secured the cooperation of Joel Greenberg, a former Gaetz associate.

• Here are 13 key people to watch as federal prosecutors close in on Gaetz.

The Justice Department's wide-ranging sex crimes investigation into Rep. Matt Gaetz of Florida advanced in dramatic fashion when Gaetz's ex-girlfriend this week testified before a federal grand jury.

Her testimony marks a significant victory for prosecutors who for months had sought her cooperation while investigating whether Gaetz, a three-term Republican, broke federal sex-trafficking laws and obstructed justice.

Investigators have already secured the cooperation of Joel Greenberg, a former Florida tax official and close associate of Gaetz's, who in 2021 pleaded guilty to six felony counts. They include sex trafficking, wire fraud, identity theft, stalking, and conspiracy.

"I think they are close to wrapping up the investigation," a source, who did not want to be identified and is familiar with the inquiry, told Insider. "They are locking in testimony for witnesses that they think are crucial for a potential trial."

Here are 13 key people to watch as investigators close in on Gaetz:

Joel Greenberg, a longtime associate of Gaetz

Greenberg is perhaps the most important witness against Gaetz. The two are longtime former associates and friends, and investigators first became interested in Gaetz while they were conducting a separate sex-trafficking probe into Greenberg.

Since he pleaded guilty last year, Greenberg's sentencing hearing has been repeatedly rescheduled, indicating that he has information of significant interest for prosecutors in connection to the Gaetz inquiry. He would likely be the star witness against the Florida congressman if Gaetz is indicted and the case goes to trial.

Among other things, Gaetz allegedly sent two financial payments through Venmo to Greenberg in 2018 that totaled $900, according to The Daily Beast. The outlet said that Greenberg then wired three financial payments to three different women through the same phone application that totaled the same amount.

Greenberg also reportedly said in a letter to the longtime GOP strategist Roger Stone that the Gaetz paid to have sex with a minor.

Gaetz's ex-girlfriend, a former Capitol Hill intern

Gaetz's ex-girlfriend used to intern on Capitol Hill. She could be a key witness as investigators build their case against the congressman. Gaetz and his girlfriend were in an open relationship in 2017 and 2018, and reports say she traveled with Gaetz and several others to the Bahamas in 2018 as part of a trip that has also drawn investigators' scrutiny.

Gaetz's former girlfriend, whose name Insider is withholding to protect her privacy, was seen entering a courthouse with her attorney last week and is said to have provided testimony to a federal grand jury in the investigation. CBS News reported that she was granted immunity before she testified last week.

Megan Zalonka, former communications director for a marijuana association

Zalonka could also be a potential witness against Gaetz if he is formally charged and the case proceeds to trial. The Daily Beast reported that Zalonka was one of several women with whom Gaetz paid to have sex.

The outlet reported that Gaetz was seen with Zalonka at an Orlando, Florida, fundraiser in 2019. At the time, she was reportedly working as an Instagram model and a paid escort.

Zalonka, who is a former communications director for the American Medical Marijuana Physicians Association, has not publicly spoken out about the Gaetz investigation or commented on the Daily Beast's reporting.

Chris Dorworth, a former member of the state legislature

Dorworth is a longtime Gaetz associate. The two men served in the Florida state legislature together.

The New York Times reported that Gaetz and Dorworth discussed inserting a third-party candidate in the 2020 Florida Senate race in order to help Jason T. Brodeur, another associate of Gaetz, win the election.Brodeur ultimately won the seat. However, Dorworth told the outlet that he did not recollect having a discussion with Gaetz about having a third candidate running for the same seat.

Dorworth joined Ballard Partners, a lobbying and public affairs firm run by Brian Ballard, a Trump ally, in 2012 but departed the firm shortly after news of the investigation into Gaetz broke.

Halsey Beshears, former Republican state legislator

Beshears began serving in the Florida State Legislature in 2012. He worked as the Florida Department of Business and Professional Regulation secretary from 2019 until his resignation last January 2021 because of health reasons.

Politico reported that Beshears was on the plane heading to the Bahamas from Florida with Gaetz and several others in 2018.

Jason Pirozzolo, a Republican donor and marijuana entrepreneur

Pirozzolo is a Florida-based hand surgeon. He also donated to Republican political campaigns.

Pirozzolo traveled with Gaetz to the Bahamas in 2018, and CNN reported that federal officials are investigating whether the surgeon tried to improperly get Gaetz to push for pro-cannabis legislation.

Sources also told CBS News that Pirozzolo paid for travel expenses, hotel accommodations, and female escorts on the Bahamas trip. Gaetz has publicly denied that he paid for sex and had a relationship with a minor.

Savara Hastings, girlfriend of Jason Pirozzolo

Hastings is an executive director at the American Medical Marijuana Physicians Association, according to her Linkedin profile.

She is also Pirozzolo's girlfriend and could be a person of interest for investigators as they probe whether Gaetz had an illegal sexual relationship with a minor.

Joe Ellicott, an associate of Greenberg

Ellicott is a close associate of Greenberg who has now pleaded guilty to several charges, including sex trafficking.

The Daily Beast reported that Ellicott and Greenberg exchanges messages using the encrypted messaging app Signal, in which Ellicott disclosed that a woman they both were associated with "knew [the minor] was underage the whole time, had sex with her, and they both went to see other guys."

Venmo and Cash App experts who could testify on payment transactions

If Gaetz is formally charged and the case goes to trial, Venmo and CashApp experts could be asked to testify before a jury, said Renato Mariotti, a former federal prosecutor.

Gaetz allegedly sent two financial payments through Venmo to Greenberg in 2018 that totaled $900, according to The Daily Beast. The outlet said that Greenberg then wired three financial payments to three different women through the same phone application that totaled the same amount.

Among other things, prosecutors may ask these experts to describe how to make a financial transaction through the applications.

"In court, you can't just assume that everyone knows what these things mean," Mariotti told Insider.

Unnamed woman Gaetz is suspected of having had sex with when she was a minor

Gaetz's alleged relationship with this woman is at the center of the sex-trafficking investigation. In addition to examining if Gaetz had sex with the girl in 2019, when she was 17 years old and a minor, investigators are also looking into whether the Florida congressman paid for her to travel with him across state lines.

If so, this could be a violation of the Mann Act, which prohibits the transportation of "any woman or girl for the purpose of prostitution or debauchery, or for any other immoral purpose" across state lines.

Democratic Rep. Darren Soto of Florida

Soto is a Democratic lawmaker representing Florida's 9th congressional district in the US House of Representatives.

He was also the boss to a former Capitol Hill intern who was in an open relationship with Gaetz in 2017 and 2018, reportedly witnessed some of the events that are under prosecutorial scrutiny, and testified to a federal grand jury last week.

Roger Handberg, interim US Attorney for the Middle District of Florida

Handberg is the federal prosecutor who is spearheading Greenberg's case. Greenberg's sentencing hearing is scheduled for March.

Last month, Attorney General Merrick Garland appointed Handberg to be the interim US Attorney for the Middle District of Florida.

Gregory Presnell, judge at the US District Court for the Middle District of Florida

Presnell is presiding over the Greenberg case. He was appointed to his role in 2000 by then-President Bill Clinton.

The Orlando Sentinel described Presnell as being a "a fourth-generation Floridian who grew up in St. Petersburg."

He graduated from the University of Florida law school with high honors in 1966, according to the outlet.

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