Fox News legal analyst Andrew Napolitano said Thursday that special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE knows President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE's tweets are a "treasure trove" for his probe into whether the president obstructed justice.

“Mueller knows that those tweets are a treasure trove and a window into Trump’s thinking,” Napolitano said on Fox News's "Outnumbered."

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Napalitano added that if any of Trump's tweets are interpreted as containing threats or rewards, then it could be viewed as witness tampering.

“Did the president send messages to people of threats, or rewards, via his tweets? People who he knew or expected would be interviewed by Bob Mueller?” Napolitano said. “And if he did, was he engaging in witness tampering?"

Napolitano's comments came shortly after a new New York Times report that said Mueller is reviewing Trump's tweets as part of his investigation into whether he obstructed justice.

The Times reported that Mueller is focusing on Trump’s tweets about Attorney General Jeff Sessions, former FBI Director James Comey and former FBI Deputy Director Andrew McCabe, each of whom the president has repeatedly criticized on Twitter.

Among other things, Trump has tweeted and said in interviews that he would not have nominated Sessions as attorney general if he knew Sessions would recuse himself from the Russia investigation.

“If you’re going to obstruct justice, you do it quietly and secretly, not in public,” Rudy Giuliani, Trump's lawyer in Mueller's Russia probe, said in a statement in response to the report.

The report from the Times comes only a few days after Giulani told Bloomberg News that he suggested to Mueller that Trump would sit for an interview only if Mueller agreed to rule out questions about obstruction of justice.