WASHINGTON -- Michael Flynn, who resigned as President Donald Trump's national security adviser just 24 days into his administration, has pleaded guilty to making false statements to the FBI, a federal crime.
The charge, which was unsealed on December 1, marks a major development in U.S. Special Counsel Robert Mueller's criminal investigation focusing on ties between Trump's 2016 presidential campaign and Russia.
The filing in U.S. federal court in Washington, D.C., dated November 30 said Flynn "willfully and knowingly" lied when he told the FBI he had not discussed U.S. sanctions imposed against Russia with Sergei Kislyak, then the Russian ambassador to the United States.
The document said the conversation happened during the transition period between the November 8, 2016, presidential election and Trump's inauguration on January 20, 2017.
Flynn, a retired U.S. Army lieutenant general who formerly served as a top intelligence official in President Barack Obama’s administration, did not respond to reporters' questions as he arrived at federal court in Washington.
His lawyers issued a statement from Flynn saying: "I recognize that the actions I acknowledged in court today were wrong, and, through my faith in God, I am working to set things right. My guilty plea and agreement to cooperate with the special counsel's office reflect a decision I made in the best interests of my family and our country."
Trump's lawyer, Ty Cobb, released a statement saying Flynn's guilty plea does not implicate anyone other than Flynn.
"The false statements involved [in the indictment] mirror the false statements to White House officials which resulted in [Flynn's] resignation in February," Cobb's statement said.
Norm Eisen, who was a top ethics lawyer in Obama's administration, said the charge is relatively light, which could indicate Flynn has offered substantial cooperation to investigators.
"In practice, that means he will be cooperating against someone more important than he is; prosecutors don't in practice consider a defendant implicating peers or subordinates alone sufficient," he told RFE/RL in an e-mail.
Because Flynn was so high up in the campaign and the White House, he must have proffered information that can be used to make the case against others, he said.
Eisen said that might include Trump's son-in-law, Jared Kushner, Trump's son Donald Jr., or someone else of similar seniority -- perhaps even Trump himself.
Flynn resigned as Trump's national security adviser in February after it was revealed he misled Vice President Mike Pence about his contacts with Kislyak.
Mueller is leading a Justice Department investigation into contacts between Trump's election campaign and other Trump associates and Russian government agents.
Flynn is the fourth person to be criminally charged in connection with the investigation. Former Trump campaign Chairman Paul Manafort and his business associate Rick Gates were indicted in October on charges that included conspiracy and lying to federal agents. Former foreign policy adviser George Papadopoulos, meanwhile, has pleaded guilty to lying to FBI agents and was cooperating with Mueller’s investigators.
In January, U.S. intelligence agencies issued a finding that the Russian government had conducted a concerted campaign to influence the 2016 election in favor of Trump.