EXCLUSIVE: Senate Republicans are demanding answers on whether confidential human sources from Justice Department agencies beyond the FBI were used on Jan. 6, 2021, while also questioning whether Inspector General Michael Horowitz thoroughly reviewed classified and unclassified communications between handlers and their sources, warning that without that review, there may be a "major blind spot" in his findings. 

Horowitz last week released his highly anticipated report that there were more than two dozen FBI confidential human sources in the crowd outside the Capitol on Jan. 6, 2021, but only three were assigned by the bureau to be present for the event. Horowitz said none of the sources were authorized or directed by the FBI to "break the law" or "encourage others to commit illegal acts." 

But now, Sens. Chuck Grassley, R-Iowa, and Ron Johnson, R-Wis., are demanding further information from Horowitz, writing to him in a letter exclusively obtained by Fox News Digital that it is "unclear" if his office reviewed the use of confidential human sources by other DOJ components during the Capitol riot. 

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"This IG report was a step in the right direction, but Senator Johnson and I still have questions the Justice Department needs to account for," Grassley told Fox News Digital. "The American people deserve a full picture of whether Justice Department sources from its component agencies, in addition to the FBI, were present on January 6, what their role was, and whether DOJ had knowledge of their attendance." 

Grassley told Fox News Digital that Horowitz and his team "must redouble its efforts to make sure it has reviewed all relevant information and provide a sufficient response to our inquiry." 

Johnson told Fox News Digital he believes the report made public last week "may have only provided a fraction of the story regarding the presence and activities of confidential human sources or undercover federal agents in Washington, D.C. on Jan. 6, 2021." 

"I urge the Inspector General’s office to be fully transparent about their work to ensure that Congress and the public have an accurate and complete understanding about what it actually reviewed," Johnson said.

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In their letter to Horowitz, Grassley and Johnson noted that the inspector general’s office received more than 500,000 documents from the Justice Department and its components as part of its investigation. 

"According to the report, your office obtained: CHS reporting, thousands of tips provided to the FBI, investigative and intelligence records from the FBI case management system, emails, instant messages, and phone records; contemporaneous notes of meetings and telephone calls; chronologies concerning the lead-up of events to January 6; after-action assessments; training materials and policy guides; and preparatory materials for press conferences or congressional testimony as well as talking points," they wrote. 

Grassley and Johnson told Horowitz "it is vital" that his office "more precisely explain what records it sought and received from all DOJ component agencies." 

Grassley and Johnson are demanding answers on whether Horowitz obtained evidence on whether other DOJ component agencies had tasked or untasked undercover confidential human sources in the Washington, D.C., area or at the Capitol building on Jan. 6, 2021. 

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They are also asking if all communications were obtained between DOJ component agency handlers and confidential human sources or undercover agents present in the D.C. area, and whether he has received classified and unclassified non-email communication platforms used by the FBI. 

Grassley and Johnson are also demanding Horowitz share all FD-1023 forms, or confidential human source reporting documents, used in the investigation with them. 

As for his initial report, Horowitz "determined that none of these FBI CHSs was authorized by the FBI to enter the Capitol or a restricted area or to otherwise break the law on January 6, nor was any CHS directed by the FBI to encourage others to commit illegal acts on January 6." 

The report revealed that the FBI had a minor supporting role in responding on Jan. 6, 2021 – largely because the event was not deemed at the highest security level by the Department of Homeland Security (DHS). 

Horowitz, though, said the FBI took significant and appropriate steps to prepare for that role. 

According to the report, there were a total of 26 confidential human sources in the crowd that day, but only three of them were assigned by the bureau to be there. 

One of the three confidential human sources tasked by the FBI to attend the rally entered the Capitol building, while the other two entered the restricted area around the Capitol. 

If a confidential human source is directed to be at a certain event, they are paid by the FBI for their time.

Republican Iowa Sen. Chuck Grassley doubled down that he believes Christopher Wray has failed his "fundamental duties" as FBI director in a blistering letter expressing he has "no confidence" in Wray’s continued leadership over the agency. 

"For the good of the country, it’s time for you and your deputy to move on to the next chapter in your lives. I’ve spent my career fighting for transparency, and I’ve always called out those in government who have fought against it," Grassley wrote in a letter to Wray on Monday morning, referring also to the FBI’s deputy director Paul Abbate. "For the public record, I must do so once again now."

Grassley went on to say he "must express my vote of no confidence in your continued leadership of the FBI. President-elect Trump has already announced his intention to nominate a candidate to replace you, and the Senate will carefully consider that choice. For my part, I’ve also seen enough, and hope your respective successors will learn from these failures," Grassley, who sits on the Senate Judiciary Committee, continued. 

The longtime Republican senator’s letter comes as Trump’s pick to lead the FBI, Kash Patel, headed to Capitol Hill on Monday to meet with lawmakers, including Grassley, and rally support for his confirmation. 

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Before the Senate could potentially confirm Patel as FBI chief under the second Trump administration, Wray would need to step down or be fired, as he is in the midst of a 10-year appointment that does not end until 2027. 

Grassley’s lengthy letter to Wray, which spans 11 pages, detailed specific examples of Wray’s "failures​​" as FBI director, which Grassley said "shattered my confidence in your leadership and the confidence and hope many others in Congress placed in you." The Iowa senator previously argued that Wray has "failed" as FBI director in a social media message posted one day after Trump nominated Patel as FBI chief. 

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Grassley pointed to the FBI’s "unprecedented raid" of Trump’s Mar-a-Lago home in Florida in August 2022 regarding classified documents as an example of Wray's failures. The Republican senator noted the raid included about 30 armed agents who were authorized to "​​use lethal force if needed" in order to execute the search warrant. 

The agents "even searched the former First Lady’s clothing drawers," Grassley continued. 

"This raid occurred despite serious questions about the need for it. President Trump apparently was cooperating with the investigation, notwithstanding liberal press reports. He voluntarily turned over 15 boxes of documents months before the FBI’s drastic escalation," Grassley continued, adding that former Secretary of State Hillary Clinton never faced such a raid "even though she and her staff mishandled highly classified information while using a non-government server."

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He also hit the FBI for acting as an "accomplice to the Democrats’ false information campaign designed to undermine my investigation of alleged Biden-family corruption."

"On August 6, 2020, as Senator Ron Johnson and I were finishing our report on the Biden family’s financial connections to foreign governments and questionable foreign nationals, you succumbed to pressure from Democrats in Congress and provided an unnecessary briefing that Democratic leadership requested in an effort to falsely label our investigation as Russian disinformation." 

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"That briefing consisted of information we already knew and information that wasn’t connected to our Biden investigation. We made clear at the time our concern that the briefing would be subject to a leak that would shed false light on the focus of our investigation. Predictably, on May 1, 2021, the Washington Post did just that, falsely labeling our investigation as Russian disinformation," he continued. 

He added that the FBI "sat on bribery allegations" against Biden when he served as vice president, as well as Biden's son, Hunter Biden, and Ukrainian officials. 

"Consistent with that FBI failure, yet another glaring example of FBI’s broken promises under your leadership is its inexcusable failure to investigate bribery allegations against former Vice President Joe Biden, while strictly scrutinizing former President Trump. You’ve repeatedly claimed you would ensure the FBI does justice, ‘free of fear, favor, or partisan influence.’ The FBI under your watch, however, had possession of incriminating information against President Biden for three years until I exposed the existence of the record outlining those allegations, but did nothing to investigate it," he wrote. 

Grassley argued that under Wray’s leadership, the FBI has also shown an "​​outright disdain for congressional oversight," including failure to provide lawmakers with information related to the "​FBI’s ongoing mishandling of sexual harassment claims" made by female employees. 

"This request was not pulled out of a hat. It was based on credible whistleblower disclosures alleging hundreds of FBI employees had retired or resigned to avoid accountability for sexual misconduct," Grassley wrote. 

The FBI also "refused" to provide information to lawmakers regarding the vetting process of Afghan nationals amid the Biden administration's botched withdrawal from the nation in 2021, Grassley added. The FBI also came under fire from Grassley for "refusing to provide information to Congress on the FBI’s ‘Richmond memo,’" which has become known as the anti-Catholic memo for depicting traditional Catholics as violent extremists. 

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"Your and Deputy Director Abbate’s failure to take control of the FBI has hindered my work and others’ work throughout multiple Congresses on matters that needed timely information, and has prevented the truth on some issues from ever reaching the American people. You’ve also shown a continuing double standard and failure to carry through on promises," Grassley wrote in his letter.

When asked about Grassley's letter, the FBI told Fox News Digital that "the FBI has repeatedly demonstrated our commitment to responding to Congressional oversight and being transparent with the American people."

"Director Wray and Deputy Director Abbate have taken strong actions toward achieving accountability in the areas mentioned in the letter and remain committed to sharing information about the continuously evolving threat environment facing our nation and the extraordinary work of the FBI."

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Trump joined NBC’s "Meet the Press" for an interview that aired Sunday, where the president-elect also slammed Wray and said the "FBI’s respect has gone way down over the last number of years."

"He invaded my home. I’m suing the country over it. He invaded Mar-a-Lago. I’m very unhappy with the things he’s done. And crime is at an all-time high. Migrants are pouring into the country that are from prisons and from mental institutions, as we’ve discussed. I can’t say I’m thrilled," Trump said during the interview. 

"I certainly can not be happy with him. Take a look at what’s happened. And then when I was shot in the ear, he said, maybe it was shrapnel. Where’s the shrapnel coming from? Is it coming from heaven? I don’t think so. So we need somebody to – you know, I have a lot of respect for the FBI. But the FBI’s respect has gone way down over the last number of years," Trump continued. 

Wray has not revealed whether he will voluntarily step down as FBI director, with Trump expected to fire Wray in order to make room for Patel as FBI director. 

Patel is a longtime Trump ally and crusader against the "deep state," who has advocated for the firings of  "corrupt actors" within the FBI, "aggressive" congressional oversight over the agency, complete overhauls to special counsels, and moving the FBI out of Washington, D.C.

Fox News Digital reached out to the White House for comment on Grassley's letter, but did not immediately receive responses.