Robert Mueller has bluntly dismissed US President Donald Trump's claims of total exoneration in the federal probe of Russia's 2016 election interference.
The former special counsel told Congress he explicitly did not clear the president of obstructing his investigation.
The televised Capitol Hill appearance, Mr Mueller's first since wrapping up his two-year Russia probe last spring, unfolded at a moment of deep divisions in the country, with many Americans hardened in their opinions about the success of Donald Trump's presidency and whether impeachment proceedings are necessary.
Republicans and Democrats took divergent paths in questioning Mr Mueller, with Mr Trump's Republican allies trying to cast the former special counsel and his prosecutors as politically motivated.
Democrats, meanwhile, sought to emphasise the most incendiary findings of Mr Mueller's 448-page report and weaken Mr Trump's re-election prospects in ways that Mr Mueller's book-length report did not.
They hoped that even if his testimony did not inspire impeachment demands, Mr Mueller could nonetheless unambiguously spell out questionable, norm-shattering actions by the president.
Yet Mr Mueller by midday appeared unwilling or unable to offer crisp sound bites that could reshape already-entrenched public opinions.
He frequently gave terse, one-word answers to questions, even when given opportunities to crystallise allegations of obstruction of justice against the president.
He referred time again to the wording in his report or asked for questions to be repeated.
He declined to read aloud hard-hitting statements in the report when prodded by Democrats to do so.
But he was unflinching on the most-critical matters.
In the opening minutes of the hearing, the chairman of the House Judiciary Committee, Jerrold Nadler, a New York Democrat, asked Mr Mueller about Mr Trump's claims of vindication in the investigation.
"Did you actually totally exonerate the president?" Mr Nadler asked.
"No," Mr Mueller replied.
Though Mr Mueller described Russian government's efforts to interfere in American politics as among the most serious challenges to democracy he had encountered in his decades-long career, Republicans seized on his conclusion of insufficient evidence to establish a criminal conspiracy between the Trump campaign and Russia.
"Those are the facts of the Mueller report. Russia meddled in the 2016 election," said Doug Collins, the top Republican on the House Judiciary Committee.
"The president did not conspire with Russians. Nothing we hear today will change those facts."
Mr Mueller, pressed as to why he had not investigated a "dossier" of claims that the Republicans insist helped lead to the start of the probe, he said that was not his charge.
That was "outside my purview", he said repeatedly.
Though Mr Mueller declared at the outset that he would be limited in what he would say, the hearings nonetheless carried the extraordinary spectacle of a prosecutor discussing in public a criminal investigation he conducted into a sitting US president.
Mr Trump lashed out early Wednesday ahead of the hearing, saying on Twitter that "Democrats and others" are trying to fabricate a crime and pin it on "a very innocent President".
Mr Trump this week feigned indifference to Mr Mueller's testimony , telling reporters in the Oval Office on Monday: "I'm not going to be watching – probably – maybe I'll see a little bit of it."