For more than a year, the Justice Department has gone hard after James B. Comey, the former F.B.I. director, using an array of rule-bending tactics in an effort to satisfy President Trump’s drive to see him charged.
In the three cases filed against Mr. Comey so far, prosecutors have improperly used search warrants to get evidence, made glaring errors in front of a grand jury and enlisted a mafia hit man in an effort to prove that Mr. Comey had broken the law.
They also considered treating The New York Times as Mr. Comey’s co-conspirator in a leak prosecution in what appeared to be a bid to breathe new life into accusations that might otherwise have been barred by the statute of limitations.
On Friday night, a new court filing added additional details to a portrait of belligerence, showing just how far investigators have been willing to roam in their pursuit of Mr. Comey.
This summer, the filing said, prosecutors hauled two workers at a New York apartment building in front of a grand jury in Florida after they refused to let an F.B.I. agent inside to serve a subpoena on one of its residents — a longtime confidant of Mr. Comey’s from whom the government wanted testimony.
The prosecutors also threatened to charge the confidant, Daniel C. Richman, with obstruction of justice for supposedly evading the subpoena, though he says that his lawyers had already agreed to accept it on his behalf.
The new documents, filed by Mr. Richman in Federal District Court in Washington, were nominally intended to support an effort by CNN to persuade a judge to unseal secret filings that the Justice Department has submitted over the past several months in a case related to the Comey prosecutions.
But the filing amounted to a bill of particulars, laying out the ways in which Mr. Richman and his lawyers believe that the Trump administration has badgered him as it continued to pursue Mr. Comey.
“Recent actions by the government suggest that the government’s interest in the covered materials is not related to a viable investigation but instead part of a harassment campaign, which undermines any law enforcement interest the government may have in sealing,” his lawyers wrote.
The Justice Department did not respond to a message seeking comment.
Mr. Richman, an Ivy League law professor who served as an aide to Mr. Comey at the F.B.I., has been at the center of a number of investigations into Mr. Comey reaching back to Mr. Trump’s first term in the White House. Prosecutors have repeatedly sought to build a case that he and Mr. Comey broke the law by working together to release information to the news media about sensitive investigations.
Most recently, Mr. Richman was summoned in September to appear in front of a grand jury in Florida where prosecutors are working on the so-called grand conspiracy case. That investigation is based on the far-fetched theory that the criminal inquiries into Mr. Trump over the past decade or so — including some that Mr. Comey worked on — were part of a single plot to sink his political prospects.
The grand conspiracy case has been marred from the outset by a lack of focus and a wave of firings and resignations of the prosecutors in charge of it. And Mr. Richman’s new court filing bolstered the picture of an investigation steeped in chaos.
The papers described “a series of unsettling and irregular communications” in which three prosecutors gave Mr. Richman different answers to the question of whether he was a target or merely a subject of the inquiry.
They also indicated that prosecutors could not quite agree about whether to grant Mr. Richman immunity before he appeared before the grand jury. Mr. Richman ultimately invoked his Fifth Amendment right against self-incrimination.
This description of prosecutors reaching for hardball tactics but fumbling at times to enact them was in keeping with the way in which the Justice Department has behaved in other cases focused on Mr. Comey.
In the first indictment filed against him, in which he was accused of lying to Congress about his dealings with the news media, prosecutors bent — and sometimes broke — the normal rules of criminal procedure. In that case, filed in Federal District Court in Alexandria, Va., three judges took issue with the Justice Department’s conduct.
One judge determined that investigators had unlawfully obtained a critical trove of evidence in the case — namely, a cache of messages exchanged by Mr. Comey and Mr. Richman — by reusing a search warrant they initially secured in a different case. Another judge found that the inexperienced prosecutor picked by Mr. Trump to bring the charges made several mistakes while presenting the case to a grand jury.
Ultimately, a third judge threw out the case after ruling that the prosecutor, Lindsey Halligan, who had once worked as Mr. Trump’s personal lawyer, had been improperly appointed to her prosecutorial post.
The second case against Mr. Comey, filed in the Eastern District of North Carolina, was similarly marked by an unusual working theory and unorthodox investigative tactics. It centered on accusations that Mr. Comey threatened Mr. Trump’s life by posting a photograph of seashells on a beach arranged to read, “86 47.” Prosecutors claim that the image showed Mr. Comey’s desire to “86” — or kill — Mr. Trump, who is the 47th president.
In seeking to prove this allegation, investigators interviewed Salvatore Gravano, a former mafia hit man. The investigators wanted Mr. Gravano’s help in making the case that Mr. Comey, who worked on mob cases when he was a young federal prosecutor, would have known that “86” was mafia slang for killing.
The third case against Mr. Comey accuses him of authorizing the release of national security information in October 2016 that prosecutors said appeared in an article in The New York Times.
Those charges were filed in a highly unusual manner, laid out in a document known as a criminal information, which can be brought by prosecutors alone without the immediate approval of either a judge or a grand jury.
Prosecutors filed the information in Washington exactly a decade after the publication of a Times article that exposed the novel use of a surveillance technique on the email platform Yahoo. Mr. Comey’s lawyers have accused the government of improperly using the information to skirt the 10-year statute of limitations in the case and have asked a federal judge to dismiss it.
But prosecutors have raised the possibility of adding additional defendants — including Mr. Richman or potentially The Times — to the case in a way that could extend the statute of limitations past October.
