President Donald Trump on Friday said fired FBI Director James Comey's reported drafting of a statement exonerating Hillary Clinton of criminal charges before an investigation into her private email server was complete is evidence of "a rigged system."

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

Trump was responding to reports about a letter sent this week by two GOP senators to current FBI Director Christopher Wray that cited testimony indicating Comey started drafting a statement recommending that Clinton not be indicted before investigators interviewed her and before former Clinton aides were granted immunity.

"Conclusion first, fact-gathering second – that's no way to run an investigation," Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, and Sen. Lindsey Graham, R-S.C., wrote in their letter to Wray. "The FBI should be held to a higher standard than that, especially in a matter of such great public interest and controversy."

The pair also requested additional information by Sept. 13 about Comey's decision, including any drafts of the statement he gave on July 5, 2016, in which he announced his recommendation that Clinton not be held criminally liable for improperly handling classified information but chastised her for being "extremely careless."

A release posted to Grassley's website says Comey appears to have started drafting a statement in April or May 2016. Sources familiar with the issue told CNN the FBI by spring had seen much of the evidence, which was trending against supporting an indictment of Clinton. A source also said Comey was not involved in the day-to-day investigation, and that a conclusion on his part would not have changed the outcome of the probe.

The FBI's investigation began in July 2015, after The New York Times first reported in March of that year on Clinton's use of a private server while serving as secretary of state.

Trump fired Comey as FBI director in May of this year.