(CNN) Former FBI Director James Comey told lawmakers in a closed-door meeting on Friday that he didn't believe firing Robert Mueller alone would derail the investigations that have been launched since he was appointed special counsel last year.

Asked by Democrats what would happen if Mueller were fired, Comey said he didn't know the effect, but predicted it wouldn't stop the underlying investigations, according to a transcript of the interview released by lawmakers on Saturday.

"You'd almost have to fire everyone in the FBI and the Justice Department to derail the relevant investigations," Comey said.

Comey also defended Mueller, who was appointed following Comey's firing as FBI director in May of last year, although the former FBI chief said that he and the special counsel were not "best friends" as President Donald Trump has claimed.

Comey testified for more than six hours behind closed doors on Friday before the House Judiciary and Oversight committees under an agreement that led to the release of the transcript Saturday.

Lawmakers and Comey said that the interview was tense and that Republicans were frustrated by instructions from a FBI attorney telling Comey not to answer certain questions about the Russia investigation. Comey and House Democrats said the interview was a waste of time, consumed with questions about Hillary Clinton's emails.

Comey was interviewed as part of the Republican-led investigation into FBI's investigations into Clinton and Trump and Russia in 2016. Republicans are preparing a report detailing their findings before Democrats take control of the House in January.

The questions from both Republican and Democratic lawmakers ran the gamut, focusing on everything from Comey's announcement on the reopening of the Clinton email investigation just days before the 2016 election to his thoughts on Trump's pick for attorney general, and to whether any pictures existed of him hugging and kissing Mueller — as Trump once claimed in an interview with The Daily Caller.

"Are you best friends with Robert Mueller?" Rep. Jerry Nadler, the top Democrat on the Judiciary Committee, asked Comey.

"I am not. I admire the heck out of the man, but I don't know his phone number, I've never been to his house, I don't know his children's names," Comey said. "I think I had a meal once alone with him in a restaurant. I like him. I am not a -- I'm an associate of his who admires him greatly. We're not friends in any social sense."

Comey also said Mueller will conduct his investigation "the right way."

"There are not many things I would bet my life on. I would bet my life that Bob Mueller will do things the right way, the way we would all want, whether we're Republicans or Democrats, the way Americans should want," Comey said.

Tidbits on the Russia probe

Much of the interview covered territory Comey has previously discussed either in past congressional testimony, his memoir , or news interviews over the past year. The interview did not contain any major revelations, but there were interesting tidbits shedding light on the tumultuous period of the FBI and Department of Justice that stretches back to the 2016 campaign.

Comey told lawmakers that the FBI launched its Russia counterintelligence investigation into four individuals, and not the Trump campaign itself.

"The Trump campaign was not under investigation," he said in response to a Democratic question asserting that it was. "The FBI, in late July, opened counterintelligence investigations of four Americans to see if they were working in any way with the Russians to influence our elections," Comey said.

There are certain clues about what Comey couldn't discuss, too. The FBI lawyer, for instance, said Comey could not answer a question about the sources used by Trump dossier author Christopher Steele, arguing that the sources for the document are still relevant to the special counsel investigation.

There was plenty of debate over the dossier, which Republicans have argued was misused by the FBI to obtain a foreign surveillance warrant on former Trump campaign aide Carter Page.

But Comey defended the application for the surveillance warrant, which he signed off on before it was obtained in October 2016.

Comey argued that the FBI didn't need to explicitly tell the court Steele's research was paid for by the Clinton campaign, only that it was politically motivated.

"The particulars of which Democrats, which Republicans, I wouldn't think would be important to the court," Comey said. "They'd want to be aware of the general bias, and that's my reaction."

Republicans focused on whether the dossier was verified before the Page warrant was obtained.

Rep. John Ratcliffe of Texas, for instance, quoted former FBI Deputy Director Andrew McCabe's testimony that the FBI "could provide no points of verification to verify the Steele information other than the fact that Carter Page had traveled to Russia in July of 2016."

But Comey said "an effort was underway to try to replicate, either rule in or rule out, as much of that collection of reports that's commonly now called the Steele dossier as possible."

Comey talks obstruction

While Comey's testimony did not shed new light on his views about whether the President obstructed justice in firing him, testimony from another former official showed those at the highest levels of the FBI were seriously concerned.

Comey was confronted with the October 2018 transcript of former FBI general counsel James Baker -- which has not been made public -- who described the "horrible atmosphere" that was filled with "shock" after Comey was fired in May 2017. Baker told lawmakers he believed that the President had fired Comey because Trump was trying to obstruct the FBI's investigation into the Russia matter, and that belief was shared by McCabe.

"The President was trying to put his finger on the scale," Baker testified -- something Comey told lawmakers on Friday he "potentially" agreed with, but would need to understand more about the President's intent before reaching a conclusion.

CNN reported this week on the circumstances that prompted McCabe to open an obstruction investigation in the wake of Comey's firing even before Mueller was appointed less than two weeks later.

Comey reiterated his prior testimony that he viewed the President asking him to let go of the investigation into former national security adviser Michael Flynn as a direction to "drop" the investigation. But an obstruction of justice probe was not opened while Comey was still at the FBI, he said.

When asked how he felt seeing Flynn plead guilty, Comey said he felt, "as a citizen, glad that (Flynn) was held accountable for his crimes and that he was assisting the United States. So it seemed to me like a just outcome."

Comey was also asked to weigh in on William Barr, Trump's pick to be his next attorney general, and said he thinks "very highly of him." Comey went on to explain that he used to work for Barr, who previously served as attorney general under President George H.W. Bush, and "probably know(s) him better than I know Bob Mueller," joking that "I probably just damned him by saying he's a friend of mine, but I respect him. ... I think he's certainly fit to be attorney general."

No fireworks in testimony

There did not appear from the transcript to be any major blowups during the interview, which was starkly different from the raucous environment at the public hearing held for former FBI agent Peter Strzok, a key figure in the Clinton and Russia probes who faced criticism for sending anti-Trump text messages.

Comey said he didn't recall the answers to many of the questions, particularly when it came to details from the Clinton investigation that occurred back in 2015 and 2016.

He did face some sharp questioning at times about his decisions as FBI director.

Republican Rep. Jim Jordan pressed Comey about not telling then-Attorney General Jeff Sessions about his meeting with Trump in which the President said to let Flynn matter go because Comey had thought Sessions was about to recuse himself.

"Why would you make that assumption?" the Ohio lawmaker asked him. "He had not recused himself. If this is something important enough for you to memorialize, talk to your top people, why not then share it with the top law enforcement official in the government?"

Comey argued it was the right move.

"Because we believed -- it turns out correctly -- that he was about to step out of any involvement, anything related to Russia," he said.

The transcript was released as part of a compromise struck by Comey and House Judiciary Chairman Bob Goodlatte, R-Virginia, who had initially subpoenaed Comey to appear behind closed doors.

Comey fought the subpoena in court, saying he would only testify if the proceedings were held in public. But he later backed down, agreeing to appear behind closed doors on the conditions that the transcript would be released as soon as possible and he would be free to speak about the interview afterward.

Comey's testimony before the committee is not finished. He has agreed to return later this month for a second round of questioning in which the committees will conduct the interview behind closed doors but then release a transcript afterward.