An ex-girlfriend of Rep. Matt Gaetz (R-Fla.) testified Wednesday in front of a federal grand jury investigating the representative for sex crimes, NBC News reports, “a major development that suggests the Department of Justice may be moving closer to indicting him.”

The ex-girlfriend, who remained purposely unidentified by NBC News, has reportedly been talking with prosecutors for months to receive an immunity deal, under which she would avoid “prosecution for obstruction of justice” in exchange for testimony in an investigation concerning whether Gaetz had sex with a 17-year-old girl for money and whether he and others later violated a law pertaining to prostitution.

Gaetz himself has never been charged and has repeatedly denied any and all accusations.

The three crimes for which Gaetz is being investigated include allegedly “sex trafficking the 17-year-old; violating the Mann Act, which prohibits taking prostitutes across state lines; and obstructing justice,” NBC News writes, per legal sources familiar with the probe.

Authorities hope testimony from the unnamed ex-girlfriend will “fill in crucial aspects” of the investigation, which began over a year ago, per NBC News. The ex is reportedly linked to Gaetz during the same period of time he’s been accused of having “sexual contact” with a woman who was 17 at the time, notes CNN. Investigators also believe the former girlfriend could prove integral regarding allegations of obstruction of justice against the lawmaker.

In May, Gaetz’ associate and “former Florida tax official Joel Greenberg pleaded guilty to several felonies and formally agreed to cooperate with the sex crimes investigation,” per Insider.