Federal prosecutors have lots of ways to intensify pressure on the people they're investigating, from early morning FBI raids to leaning on relatives of those under government scrutiny.
But even by those measures, the special counsel investigating Russian interference in last year's presidential election is moving with unusual speed and assertiveness, according to half a dozen legal experts following the probe.
Consider disclosures that FBI agents executed a search warrant last month for business and tax records at the suburban Virginia home of former Trump campaign chairman Paul Manafort. That step would have required them to prove to a judge that there's probable cause a crime has been committed.
Kenneth Starr, the Whitewater independent counsel frequently criticized for alleged overreach by then-President Bill Clinton, never utilized search warrants, two members of the team told NPR. Neither did the special counsel investigating the leak of a CIA operative's identity in the George W. Bush administration, said William Jeffress, a Washington attorney who represented White House aide Lewis "Scooter" Libby in that probe.
"A search warrant in a case like this is highly unusual," Jeffress said.
Lawyers said the special counsel may have been motivated to use a search warrant over concerns that evidence might be concealed or destroyed, which sometimes happens in terrorism and drug trafficking cases. Or, they said, Mueller may have been moving quickly amid a series of existential threats. In recent weeks, President Trump has blasted the Russia investigation as a "witch hunt" and flirted with the idea of firing Justice Department leaders as a roundabout way to get rid of Mueller himself.
Talking with reporters Thursday, the president said he was "very surprised" by the FBI raid at Manafort's home and said it sent a "strong signal." Trump also said that the White House is cooperating with the special counsel probe even though, he said, the subjects under investigation never happened.
In any case, the Justice Department frequently deploys tough tactics with a larger goal in mind: securing the cooperation of insiders who can guide authorities through a complex investigation and help deliver bigger targets.
"I call it 'climbing the ladder,' " Jeffress said. "It happens in every corporate investigation," where investigators question clerks and assistants, and then move up to vice presidents and higher-level executives.
A spokesman for Manafort, Jason Maloni, said he is responding to government inquiries.
Whether Manafort, former Trump national security adviser Michael Flynn or anyone else decides to strike a deal with the government is being closely watched by people in and outside the probe.
Authorities routinely enlist relatives to try to turn up the heat. Recent media reports suggested that investigators have reached out to Manafort's son-in-law, with whom he'd entered into some real estate dealings.
Indeed, several members of Mueller's 16-lawyer special counsel team have a long history of approaching lower-level figures, including spouses and in-laws, to build bigger cases.
Take Andrew Weissmann, a special counsel lawyer who once led the Justice Department's Enron Task Force. Prosecutors looking to uncover and punish fraud at that defunct energy company famously threatened to charge the wife of the company's chief financial officer with tax offenses if he did not agree to plead guilty and testify against his corporate superiors. The finance official, Andrew Fastow, refused. So, authorities indicted his wife, Lea. They both served prison time.
A more recent addition to the special counsel team, Greg Andres, helped bring to justice the Bonanno crime family boss as a young mob prosecutor in Brooklyn, N.Y. Through the course of the trial, Andres helped unravel dozens of crimes over three decades, using federal agents and members of the crime family as narrators. One of his key witnesses was the brother-in-law of the defendant, Joseph Massino.
"The story principally was told from the vantage point of those involved in the crimes at issue and their credibility was a crucial issue," Andres told the publication Law360 last year.
Andres so got under the skin of the mobsters that one later testified he had been targeted for a "hit."