On Friday, Dec.1, Michael Flynn, a former Army lieutenant who served as Trump’s national security advisor, pleaded guilty to lying to the Federal Bureau of Investigation (F.B.I) in the midst of the Russian election-interference investigation.

Flynn’s hearing occurred at federal court in Washington, D.C. on Friday morning. He became the fourth person charged in Special Counsel Robert Mueller’s current investigation. Flynn has agreed to cooperate with federal prosecutors. This can require interviews, providing true written statements, a polygraph exam and other judicial processes. Mueller agreed to request a reduce in sentencing if Flynn provides “substantial assistance.”

Mueller is charging Flynn with one count of lying to the F.B.I. He apparently escaped a number of charges from other cases. The maximum penalty for false statements is five years, but court documents show that he will probably face only up to six months in prison. No date has been set yet for sentencing.

Flynn’s lies to the FBI are reported to span from December 2016 to March 2017. He has admitted to multiple specific fraudulent statements, including that he did not ask Russia’s ambassador to the US, Sergey Kislyak, to “refrain from escalating the situation in response to sanctions that the United States had imposed.” He additionally admitted to lying on foreign agent registration materials. Flynn, who claims remorse for his actions, did not communicate in documents whether President Trump was aware.

“After over 33 years of military service to our country, including nearly five years in combat away from my family, and then my decision to continue to serve the United States, it has been extraordinarily painful to endure these many months of false accusations of ‘treason’ and other outrageous acts,” Flynn stated.

He also reported that his lies are contrary to everything he has stood for and accepts full responsibility for his actions. His decision reflects the best interest of his family and his country, he said.

Reportedly, Trump asked former F.B.I. director, James B. Comey, to shut down the investigation just a day after Flynn was fired. A possible motive for the President’s attempt to halt investigation would be to avoid revealing the involvement of his officials in Flynn’s discussions with Kislyak. Trump made no comments to the public after Flynn’s hearing this past Friday.