The statement warned reporters to "be very cautious about any source that claims to have knowledge about our investigation and dig deep into what they claim before reporting on it."
It was a rare statement from an office that has remained almost silent as the world's media closely followed the investigation, and often relied on anonymous sourcing to characterize what Mueller and his staff were doing.
The statement said to journalists: "If another outlet reports something, don't run with it unless you have your own sourcing to back it up."
Trump has claimed victory as his staunchest critics were left disappointed by Attorney General William Barr's summary of the Mueller report, which was delivered to Congress on Sunday.
In the summary, Barr found that neither Trump nor his presidential campaign conspired or colluded with Russia to influence the election.
But Mueller did not reach a conclusion as to whether Trump obstructed justice, and Mueller also said that "while this report does not conclude that the President committed a crime, it also does not exonerate him."
But the immediate effect of the report dropping was to puncture expectations that the report could prove collusion, lead to high-level indictments, and potentially even end Trump's presidency.
Journalist Glenn Greenwald, a long-term critic of the idea that Mueller's report would prove collusion, tweeted on Sunday that outlets like CNN and MSNBC had committed a "massive error" in their reporting.
"Check every MSNBC personality, CNN law 'expert,' liberal-centrist outlets and scam artist and see if you see even an iota of self-reflection, humility or admission of massive error," he tweeted.
And Tim Graham, director of media analysis for the conservative Media Research Center, was cited by The Washington Post being similarly dismissive.
He said: "liberal journalists expected Mueller to build a case for scandalous collusion between the Trump campaign and the Russian government."
"So now its apparent the news channels merely channeled their wishful thinking. They had a grand denouement in mind, and it didnt happen. They mocked Trump for saying no collusion, and that ended up being the truth."
Former officials, Democrats, and even Trump stoked claims that the Mueller report could be devastating for Trump
Much of the reporting that Mueller could prove a heavy blow to Trump was based on predictions and comments from Democrats and former officials who spoke about the investigation.
Former CIA Director John Brennan suggested to MSNBC in March that a member of the Trump family could be weeks from getting.
Top Democrats said that Trump could be jailed or impeached as part of the investigations into him.
And Trump's own lawyer, Rudy Giuliani, left open the possibility thatTrump's 2016 election campaign could have colluded with Russian operatives when speaking to CNN in January.
These comments continued to fuel a narrative that Mueller's report would find evidence of collusion, potentially devastate Trump, and could even provide evidence that could kick off an impeachment process.
Dean Baquet, the executive editor of The New York Times, answered questions about his paper's coverage, by saying that stories it published about Russians trying to contact Trump were "true."
"On Russia interference, we and others wrote extensively about Russias attempt to influence the election, both through hacking and direct approaches by Russians to people around candidate Trump," Baquet told the Post.
"Those stories were true", Baquet said. "And nothing has happened to call into question the reporting about Donald Trumps financial history, or the use of his charity, or any of the other fine investigative reporting over the past three years."
"Im comfortable with our coverage. It is never our job to determine illegality, but to expose the actions of people in power. And thats what we and others have done and will continue to do."
Mueller's office has largely stayed quiet about reports on the probe. But it did dispute a January BuzzFeed News report that said Mueller had evidence that Trump directed Michael Cohen to lie to Congress, which the outlet stands behind.
"BuzzFeed's description of specific statements to the Special Counsel's Office, and characterization of documents and testimony obtained by this office, regarding Michael Cohen's Congressional testimony are not accurate," spokesman Peter Carr said in a statement to INSIDER .
And outlets like Politico and The Atlantic warned months ago that the final report may ultimately be just a short summary, and that Mueller would likely stay quiet afterward.
