Federal prosecutors concluded a central witness would actually undermine their case against former FBI Director James Comey, according to reporting.

Law professor Daniel Richman, who prosecutors allege Comey authorized to leak information to the media, told investigators the former FBI director had instructed him at least twice not to engage with journalists and unequivocally did not authorize him to provide information to a reporter before the 2016 election, according to sources who spoke to ABC News.

"According to prosecutors who investigated the circumstances surrounding Comey's 2020 testimony for two months, using Richman's testimony to prove that Comey knowingly provided false statements to Congress would result in 'likely insurmountable problems' for the prosecution," the network reported.

Investigators stated their concerns about the case last month in a lengthy memo advocating against criminal charges, according to sources familiar with the document, but President Donald Trump replaced the lead investigator with a loyalist aide, Lindsey Halligan, who quickly presented the case to a grand jury and secured an indictment.

Halligan alleges that Comey intentionally misled Congress in 2017 and 2020 when he testified that he'd never authorized anyone to provide information anonymously to reporters, but Richman told investigators last month that he had never served as an anonymous source or acted on Comey's direction when he led the FBI, and he said Comey told him at least twice specifically not to speak with the press.

Investigators who looked at material from Comey's emails, including messages to Richman, could not find any instance where he approved the anonymous leak of information to a reporter, sources said.