(CNN) Attorney General William Barr on Tuesday discarded a key finding of the 435-page report released by the Justice Department's watchdog , saying in an interview that the FBI may have acted in "bad faith" when they carried out an investigation into President Donald Trump's campaign in 2016.

"I think our nation was turned on its head for three years, I think, based on a completely bogus narrative that was largely fanned and hyped by an irresponsible press, and I think that there were gross abuses of FISA and inexplicable behavior that isn't tolerable in the FBI," Barr told NBC News.

The Horowitz report released on Monday found that the FBI had properly opened its investigation , and the inspector general wrote that he found no evidence that bias influenced certain significant decisions made throughout the case.

Barr had remained largely quiet as the investigation by Inspector General Michael Horowitz wound toward a conclusion in recent weeks, but in the interview Tuesday he revealed deep mistrust of the premise of the Russia probe and indicated that the final word on FBI misconduct would not come until the investigation by John Durham , a veteran Justice Department prosecutor who he picked to lead the separate probe, was finished -- perhaps as soon as in the late spring.

Barr excoriated the FBI for making mistakes and omissions as they sought to surveil former Trump campaign aide Carter Page, in line with the findings of the Horowitz report.

But Barr took his criticism further, telling NBC that the FBI could have acted maliciously as they continued to seek out surveillance of the Trump campaign despite certain pieces of evidence that had been used to stand it up in court -- like elements of the intelligence gathered by Christopher Steele -- falling apart.

"They not only didn't tell the court that what they had been relying on was completely rubbish, they actually started putting in things to bolster the Steele report," Barr said. "That's hard to explain. The core statement in my opinion by the IG is that these irregularities, these misstatements, these omissions were not satisfactorily explained. I think that leaves open the possibility to infer bad faith."

"I think it's premature now to reach a judgment on that but I think that further work has to be done and that's what Durham is doing," he continued.

The inspector general can only compel DOJ employees to cooperate with his investigation, and Barr described his protocols as "very deferential."

"[Horowitz's] approach is to say, if I get an explanation from the people I'm investigating that is not unreasonable on its face, then I will accept it as long as there's not contradictory testimonial or documentary evidence... And all he said is people gave me an explanation. And I didn't find anything to contradict it. So I don't have a basis for saying that there was improper motive. But he hasn't decided the issue of improper motive," Barr said.

In an interview with ABC News on Monday, FBI Director Christopher Wray lamented "actions described in this report that [he] considered unacceptable and unrepresentative of who we are as an institution."

But Wray added that he thought it was "important that the inspector general found that, in this particular instance, the investigation was opened with appropriate predication and authorization."

President Donald Trump earlier Tuesday lashed out at Wray in a tweet, writing, "I don't know what report current Director of the FBI Christopher Wray was reading, but it sure wasn't the one given to me. With that kind of attitude, he will never be able to fix the FBI, which is badly broken despite having some of the greatest men & women working there!"

Barr told NBC that he had confidence in Wray and believed he was "working hard to address the problems of the past." But Barr appeared to ding Wray's reaction to the report and side with Trump, adding that "we can't ignore the abuses of the past and appear to be justifying them or minimizing them."

Barr, as the head of the Justice Department, oversees the FBI.

Barr also reiterated his opinion that the FBI did not have enough evidence to open up a full investigation into the Trump campaign in 2016 -- which diverges from the conclusion reached by Horowitz.

According to the Horowitz report, the FBI investigation -- codenamed Crossfire Hurricane -- was opened exclusively on a tip to the FBI from an Australian diplomat that George Papadopoulos, then a foreign policy aide on the Trump campaign, had displayed knowledge of a possible plan by the Russians to release information damaging to Hillary Clinton.

In the interview, Barr dismissed Papadopoulos as a "28-year-old campaign volunteer" and suggested that the information he communicated could have been conflated with contemporaneous news reports about Russian hacking.

Papadopoulos has said that he actually received the information on the Russians possessing "dirt" on Clinton from a Maltese professor who is said to be connected to Russian intelligence.

Barr downplayed the importance of any communication between a political campaign and a foreign government at all -- saying it's a frequent occurrence in modern elections -- and focused his criticism on the Obama administration for admonishing the Russian government about their meddling while declining to directly question the Trump campaign about any potential collusion.