By Adam Goldman and Eileen Sullivan

New York Times News Service

WASHINGTON — Michael T. Flynn, President Donald Trump’s first national security adviser, helped substantially with the special counsel’s investigation and should receive little to no prison time for lying to federal investigators, according to court documents filed Tuesday.

Prosecutors for the special counsel, Robert Mueller, described Flynn as a key cooperator who helped the Justice Department with several investigations, sitting for 19 interviews with Mueller’s office and other prosecutors and handing over documents and communications.

“His early cooperation was particularly valuable because he was one of the few people with long-term and firsthand insight” into the subject of Mueller’s investigation — Russia’s election interference and whether any Trump associates conspired, prosecutors wrote in a sentencing recommendation memorandum and an addendum that was heavily blacked out.

In particular, they wrote, he may have prompted others to cooperate with the inquiry. “The defendant’s decision to plead guilty and cooperate likely affected the decisions of related firsthand witnesses to be forthcoming,” prosecutors said.

They also indicated that Flynn helped with other investigations without revealing details about them.

Flynn, who served briefly as the president’s national security adviser, is the only White House aide and the first person from the president’s inner circle to strike a cooperation deal with the special counsel’s office in exchange for a more lenient penalty. He pleaded guilty a year ago to lying to the FBI about conversations he had with the Russian ambassador to the United States at the time, Sergey Kislyak.

“The defendant deserves credit for accepting responsibility in a timely fashion and substantially assisting the government,” prosecutors wrote.

The cases of some other former Trump aides caught up in the special counsel investigation are also nearing resolution, marking an active week for Mueller’s inquiry. By Friday, Mueller’s prosecutors are due to enumerate how they believe Paul Manafort, Trump’s former campaign chairman, violated a plea agreement and separately to outline the extent of cooperation by Michael Cohen, Trump’s longtime lawyer and fixer.

Another longtime Trump associate whom Mueller is scrutinizing, Roger Stone, said Tuesday that he had invoked his Fifth Amendment rights in response to a request from Democratic investigators for the Senate Judiciary Committee to hand over documents and testimony relevant to their own Russia inquiry. Stone’s lawyer, Grant J. Smith, said the committee’s request was “overbroad” and stressed that Stone was “an innocent citizen who denounces secrecy.”