Federal prosecutors in U.S. Attorney Jeanine Pirro’s office are dropping a criminal probe into whether former President Joe Biden and his aides unlawfully used an autopen to issue pardons, a person briefed on the matter told CBS News.

Two sources confirmed the existence of the probe, with one telling CBS News that the matter has since been closed because prosecutors were never able to find a legal hook to be able to pursue the matter further. CBS News has not determined precisely when the case ended.

Last June, President Trump ordered an investigation into whether the Biden administration used an autopen machine to sign key presidential documents like pardons — months after Mr. Trump had claimed his predecessor’s pardons were illegitimate.

Mr. Trump told Attorney General Pam Bondi and the White House counsel in a memo to probe what he claimed was a “conspiracy” to “abuse the power of Presidential signatures through the use of an autopen to conceal Biden’s cognitive decline.”

The order cited a number of executive actions by Biden, including pardons and judicial appointments, and argued “there are serious doubts as to the decision making process and even the degree of Biden’s awareness of these actions being taken in his name.” 

It suggested that if Biden’s advisers “secretly used the mechanical signature pen,” it would “have implications for the legality and validity of numerous executive actions.”

Biden at the time called the attacks false and “nothing more than a distraction by Donald Trump and Congressional Republicans.”

The closed autopen probe represents one of several failed attempts in recent months by Pirro’s office to pursue cases against Mr. Trump’s political enemies. 

Recently, a grand jury also refused to indict six Democratic lawmakers over charges they violated the law by urging military service members to reject unlawful orders in a video they released last fall, CBS previously reported. In that matter, not a single grand juror voted in favor of an indictment, which is highly unusual.

Pirro’s office has also sought to subpoena records from the Federal Reserve over its renovations and comments that Chairman Jerome Powell made about those renovations in testimony before Congress. The Federal Reserve is quietly seeking to quash those subpoenas, in a closed-door legal fight that remains under seal due to grand jury secrecy rules, CBS News previously reported.

The New York Times first reported on the closure of the autopen review. CBS News has asked for comment from the Justice Department. 

On Thursday, Pirro posted on X, “We cannot comment on ongoing investigations.”