President Trump's former personal attorney John M. Dowd told Fox News that the Justice Department watchdog's report on the FBI's actions in the Clinton email investigation wasn't nearly tough enough on fired FBI Director James Comey.

In the report released Thursday, Justice Department Inspector General Michael E. Horowitz called Comey "insubordinate" and deviating from "well-established department policies."

Dowd told Fox News in an email, "The clear evidence of his usurpation of power, violation of his oath of office and material false statements to the public and the Congress all to conceal his own misconduct warranted a criminal referral of Comey’s conduct. The finding of no bias was ludicrous. The OIG findings support the President’s decision to fire Comey."

He also told Fox News that Deputy Attorney General Rod Rosenstein and Special Counsel Robert Mueller "allowed their relationship with Comey over the years [to] blind them to his obvious appalling behavior. I was shocked that Mueller chose not to investigate the President’s accuser before investigating the President, who you will recall was 'not under investigation' according to the sworn testimony of Comey. As a result, the authenticity and legality of the Mueller investigation is in serious question and should no longer be honored."

Trump himself told Fox News' Steve Doocy on "Fox & Friends," "I think Comey was the ringleader of this whole den of thieves."

Letters newly obtained by Fox News, which were written in the summer and fall of 2017, revealed Dowd and another Trump attorney, Marc Kasowitz, had deep reservations about Comey's credibility as the main witness, called Witness #1, in the ongoing Russia collusion probe that started shortly after Trump fired Comey on May 9, 2017.

In a blistering 13-page letter hand-delivered to Mueller on June 27, Kasowitz elaborated his concerns about Comey, whom he called "Machiavellian," after the former FBI director testified before the Senate Select Committee on Intelligence. Kasowitz wrote Comey was an "FBI director unbounded by law and regulation, driven by his own interests and emotions, willing to provide embellished and incorrect testimony..."

Pushing back on Comey's promise to the president of "honest loyalty" as FBI director, Kasowitz wrote that Comey was "surreptitiously leaking to civilians his privileged and confidential conversations with the President, or misappropriating and disseminating his confidential FBI memos or their contents about those meetings."

Neither the DOJ nor the office of the special counsel commented on the letters when contacted by Fox News.

New details of Comey's reliance on his friend and go-between leaker to the media, Columbia law professor Daniel Richman, were revealed in a footnote of the OIG report.

Fox News reported about Richman's rare approval for special government employee clearance by Comey in April.

Fox News reached out to Richman for comment on the new OIG report, but he did not respond.

In the new email to Fox News, Dowd called Comey's relationship with Richman "deceitful" and "a complete disrespect and subversion of the normal processes we rely on the govern the FBI/DOJ."

In the letter that Dowd wrote on September 1, 2017 to Rosenstein, there was a direct request for a "Federal Grand Jury Investigation of Former FBI Director James B. Comey." Dowd wrote, "It appears the fix was in, a cover-up is in place and the reputations of the FBI and the Department of Justice are tarnished and hang in the balance."

Specifically, Dowd charged in in the letter that "Director Comey drafted his unauthorized, improper and dishonest conclusion to the Clinton e-mail investigation three months before the clearly superficial and inadequate investigation was conducted."

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Fox News learned that the DOJ acknowledged Dowd's letter but took no further action.

Meanwhile, hours after the OIG report was released, Comey accepted the findings and was active on Instagram -- posting a picture of himself with a giant gnome statue in Iowa. He tweeted the photo Friday.