The former special counsel, who had spent nearly two years probing allegations that US President Donald Trump colluded with Russia and obstructed investigations, did not advance the findings in his April report or tie up the loose ends during about seven hours of testimony on Wednesday.
Trying to stay above the partisan fray, he neither made the strong case for impeachment that the Democrats wanted nor granted the complete exoneration of Trump that the Republicans sought.
"The report is my testimony," Mueller said, refusing to yield to either side for the most part, with "I can't speak to that" being a frequent refrain in separate testimonies before the House of Representatives Judiciary and Intelligence Committees.
Both Trump and his Democratic nemesis, Speaker Nancy Pelosi, claimed victories at the end of the day.
"It was a great day for me," Trump told reporters. "This was a devastating day for the Democrats".
"What we saw today was a very strong manifestation in fact, some would even say indictment of this administration's cone of silence and their cover-up," Pelosi said at a news conference.
Without a blockbuster revelation from Mueller, she ruled out, for now, an impeachment of Trump on charges of obstructing justice by interfering with the probe or alleged collusion with Russia.
"My position has always been whatever decision we made in that regard would have to be done with our strongest possible hand, and we still have some outstanding matters in the courts," she said.
Eightynine of the 235 Democratic representatives support impeachment and Pelosi faces pressure from the progressive wing of her party to proceed with it.
She fears that an impeachment would be a futile distraction in an election year because while the Democratic-controlled House can impeach Trump, ultimately the Republican-majority Senate will have to accept it and vote to remove him from office - an unlikely scenario.
Pelosi favours multi-pronged investigations of Trump, his family and his associates by the Congressional committees and court cases to build the case against him.
If there is ultimately an impeachment, Pelosi said, "The stronger our case is, the worse the Senate will look for just letting the president off the hook."
Mueller said that while the current position was that a sitting president cannot be criminally charged in court, the official could be tried after leaving office.
Mueller did agree with the Democrats that "generally" Trump wasn't truthful in his written testimony, And he said that his "finding indicates that the president was not exculpated for the acts that he allegedly committed."
Mueller was emphatic about Russian interference in the 2016 election, warning that it was happening "as we sit here."
But he also said, "We found insufficient evidence of the president's culpability" or his campaign's in conspiring with Russia during the elections.
And that was the rationale for Trump's and his supporters' elation.
Republican representatives unsuccessfully pressed Mueller about a former British intelligence agent. Christopher Steele, whose dossier on Trump that was paid for by the Democrats and was a basis for the start of the Federal Bureau of Investigation into Trump campaign's alleged links to Russia.
Republicans maintain that the dossier based on dubious Russian sources as well reports of an Australian diplomat's conversation with a junior Trump campaign worker, George Papadopoulos, in London laid the grounds for the FBI probe that ultimately led to the Mueller investigation. (Papadapoulos was later found guilty of lying to investigators.)
Mueller said the matters around the dossier were outside his purview.
Mueller, who was the FBI director during the 9/11 terrorist attack and a dozen year afterward, serving Republican and Democratic presidents, appeared tired and faltered at times during the hearings.
Many of the questions by members of both parties appeared to be aimed at generating campaign sound bites, rather than eliciting actionable evidence from a cagey witness. Mueller refused requests to read from his report lest they appear in campaign videos.
(Arul Louis can be reached at arul.l@.in and followed on Twitter @arulouis)
( With inputs from IANS )