The U.S. attorney’s office in New York is exploring whether it can charge Harvey Weinstein with violating federal sex-trafficking laws, as several state-level probes appear to have stalled.

Federal prosecutors were already investigating allegations that Weinstein improperly benefited from donations to amfAR, the AIDS charity he has long supported. Now investigators are also examining whether the disgraced producer violated federal law by luring women across state lines for unlawful sex, according to a report in the Wall Street Journal.

The U.S. attorney’s office declined to comment. Weinstein’s camp was not immediately available for comment.

Weinstein has consistently denied allegations of non-consensual sex. A federal case might be more difficult to prosecute than the sexual assault cases that have been presented to local prosecutors, as the U.S. attorney’s office would have to establish federal jurisdiction.

The New York Police Department has investigation allegations that Weinstein raped actress Paz de la Huerta twice in 2010. The department’s Special Victims Unit also interviewed Lucia Evans, who has alleged that Weinstein forced her to perform oral sex during an audition in 2004. New York investigators have said they are ready to arrest Weinstein, but have grown frustrated at inaction from Manhattan D.A. Cyrus Vance Jr.

Vance has also been faulted for failing to file charges against Weinstein in 2015, when Italian model Ambra Battilana alleged that he groped her and propositioned her in his Weinstein Co. office.

The L.A. County District Attorney’s office is also reviewing five cases submitted by the Los Angeles and Beverly Hills police departments. No decisions on whether to prosecute have yet been made on those cases. Weinstein is also under criminal investigation in London.