The FBI disclosed it used grand jury subpoenas more extensively during the investigation regarding former Secretary of State Hillary Clinton's email server than was previously revealed, according to a report Wednesday.

Grand jury subpoenas were used in the process of accessing Clinton's records from her accounts, and also those of people she communicated with, a top FBI official divulged in a court filing.

"In instances where the FBI discovered evidence of the potential unauthorized transmission of classified information from the [Clinton] personal email servers to private third party email accounts of individuals with whom Secretary Clinton corresponded and could establish sufficient probable cause, the FBI sought additional legal process, to include grand jury subpoenas, in order to obtain additional e-mails relevant to the FBI's investigation," Bill Priestap, the bureau's assistant director for counterintelligence, wrote in a declaration filed in federal court in Washington, Politico reported.

Many Republicans and Trump have questioned how detailed and accurate former FBI Director James Comey's investigation had been.

"Wow, looks like James Comey exonerated Hillary Clinton long before the investigation was over … and so much more. A rigged system," Trump tweeted on Sept. 1.

Trump fired Comey in May.

The investigation of the Clinton emails concluded in July 2016 and the FBI did not recommend any criminal charges against Clinton. Upon closing the case, Comey received pushback from some who said he did not use any mandatory legal process in the inquiry.

In response, Comey stated grand jury actions are classified and must be kept covert.

Freedom of Information Act releases indicated that grand jury subpoenas were used, however. This was confirmed in April by Priestap, who said they were used to retrieve messages that service providers could have stored from Clinton's account on her BlackBerry from January to March 2009.

Comey reopened the Clinton investigation on Oct. 28, 2016, days before the 2016 presidential election, but shortly after concluded that the new batch of emails the FBI found did not change the agency's conclusion.