The FBI months ago gathered what agents believed was sufficient evidence to charge Hunter Biden, the president’s son, with crimes related to taxes and making a false statement when purchasing a gun, according to sources familiar with the investigation.

Evidence gathered by FBI and IRS investigators was sent to the U.S. Attorney’s office in Delaware, according to the sources.

A spokesperson for the Trump-appointed U.S. Attorney in Delaware declined to comment. The Washington Post was first to report that the agency had provided evidence of alleged crimes to federal prosecutors.

Chris Clark, an attorney for Biden, criticized the FBI in a statement to CBS News, accusing someone within the agency of leaking information from grand jury proceedings, which would be a felony he expects “the Department of Justice will diligently investigate and prosecute.”

“As is proper and legally required, we believe the prosecutors in this case are diligently and thoroughly weighing not just evidence provided by agents, but also all the other witnesses in this case, including witnesses for the defense.  That is the job of the prosecutors,” Clark said.

A source close to Hunter Biden told CBS News that Biden’s team believes that this leak was driven by frustration inside the FBI over the time it is taking prosecutors to deliberate over this case. Biden’s team believes the bureau is trying to pressure prosecutors to act.

The FBI has been facing increasing pressure from Republicans in Congress over assertions that it is making decisions based on political considerations.

The U.S. attorney’s office in Delaware has been investigating Hunter Biden since at least 2019. A federal subpoena from that year, obtained by CBS News, sought Hunter Biden’s bank records dating back to 2014, when Joe Biden was vice president. Investigators have examined whether Biden owes taxes on income from a controversial stint, during his father’s vice presidency, as a board member for Burisma, a Ukrainian energy company, according to sources familiar with the matter.

CBS News reported in May that Biden had garnered financial backing from high-powered Hollywood attorney Kevin Morris, who sources said paid Biden’s past-due tax debts.

A December 2020 subpoena requested documents as far back as January 2017, “regarding (Hunter) Biden’s income, assets, debts, obligations, and financial transactions… and all personal and business expenditures.”

The subpoena also requested “all federal, state, local and foreign tax documentation related to (Hunter) Biden.”

Prosecutors investigating Hunter Biden also subpoenaed documents from a paternity lawsuit that included his tax records, according to documents and an attorney involved in the matter.

The investigation into Hunter Biden’s finances has been led by U.S. attorney David Weiss, who was appointed by then-President Donald Trump in 2018. He had been acting head of the Delaware office at the time and received the endorsements of the state’s U.S. Senators Tom Carper and Chris Coons, both Democrats.

In February 2021, soon after Biden took office, dozens of federal prosecutors appointed by Trump were asked to resign, but then-acting attorney general Monty Wilkinson asked Weiss to remain on the job, a Justice Department official told CBS News.

Mr. Biden has said he was not involved in his son’s business dealings, and there has been no evidence that has emerged to refute this.

“I have not taken a penny from any foreign source, ever, in my life,” Mr. Biden said in October 2020 at a presidential debate.