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WASHINGTON (CBSMiami/CNN) – Former Trump national security adviser Michael Flynn has pleaded guilty to lying to federal investigators regarding his interaction with then-Russian Envoy Sergey Kislyak.

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Afterwards he issued a statement which read in part:

“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. I accept full responsibility for actions.”

Read: Criminal Complaint Against Michael Flynn

As part of the plea, dealing Flynn will testify that senior members of Trump’s transition team wanted him to make contact with Kislyak and the Russians to talk about sanctions and how not to escalate the situation between the United States and Russia following sanctions that had been put forth by the Obama administration.

Flynn is the first Trump administration official and the fourth connected to the campaign to be charged as part of Mueller’s investigation into possible collusion between the Russian government and members of Trump’s team, as well as potential obstruction of justice and financial crimes.

Trump’s former campaign chairman Paul Manafort and his deputy Rick Gates were indicted last month; they pleaded not guilty. And Trump campaign foreign policy adviser George Papadopoulos pleaded guilty to making a false statement to the FBI over contacts with officials connected to the Russian government.

Flynn’s lawyers have previously criticized media reports about his connection to the Russia investigation as peddling “unfounded allegations, outrageous claims of treason, and vicious innuendo directed against him.” Flynn hasn’t spoken publicly since his ouster in February.

The charges mark yet another stunning downfall for Flynn, 58, a retired general who rose to the highest ranks of the Army over a three-decade career — only to see him drummed out of the military by the Obama administration before unexpectedly rising again on the heels of Trump’s election victory.

A key campaign surrogate and adviser during President Donald Trump’s presidential campaign, Flynn was tapped as Trump’s national security adviser in November 2016, a senior White House job that put him in a vital role for all of the administration’s national security and foreign policy decisions.

Though he wasn’t initially considered for the top job, Trump’s daughter, Ivanka Trump, and son-in-law Jared Kushner made it clear to the Trump transition team that they wanted him there.

Flynn would hold the job less than a month, resigning from the post after he misled Pence and then-chief of staff Reince Priebus about his conversations with Kislyak in which they discussed U.S. sanctions against Russia.

Flynn is also the spark of potential trouble for the President in Mueller’s probe, as the special counsel is investigating potential obstruction of justice in the firing of FBI Director James Comey.

Comey testified before the Senate intelligence committee that Trump asked him to drop the Flynn probe during a February Oval Office meeting not long after Flynn resigned as national security adviser.

Talking about sanctions

Flynn’s conversations with Kislyak attracted scrutiny from federal investigators as part of the FBI’s broader counterintelligence investigation of Russian activities in the US, and the calls were captured by routine US eavesdropping targeting the Russian diplomat, CNN has reported.

The Trump transition team acknowledged that Flynn and Kislyak spoke on the day in December 2016 that the Obama administration issued new sanctions against Russia and expelled 35 diplomats, but they insisted the conversation did not include sanctions — including denials that Pence and Priebus later repeated on national television.

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Flynn resigned on February 13 after reports that he and Kislyak had spoken about sanctions and that the Justice Department had warned the White House that Flynn was potentially vulnerable to blackmail by the Russians.

Details of how the DOJ warned the White House about Flynn’s conduct were revealed months later in stunning testimony from former acting Attorney General Sally Yates, who said that she “believed that General Flynn was compromised with respect to the Russians” because of the misleading denials.

The charging document states that Flynn made a false statement to the FBI when he stated that in December 2016 he did not ask Kislyak “to refrain from escalating the situation in response to sanctions that the United States had imposed against Russia that same day; and Flynn did not recall the Russian ambassador subsequently telling him that Russia had chosen to moderate its response to those sanctions as a result of his request.”

The document also says that Flynn falsely said he did not ask Kislyak to delay the vote on a pending United Nations Security Council resolution.

After his resignation, Flynn and his businesses quickly became a major interest of the House and Senate intelligence committee Russia probes.

But in March, Flynn’s lawyer dropped a bombshell: “General Flynn certainly has a story to tell, and he very much wants to tell it, should the circumstances permit,” attorney Robert Kelner said, adding that Flynn was seeking immunity in exchange for his testimony. Committee leaders quickly rejected the offer.

Both committees eventually subpoenaed Flynn and his lobbying business, and he provided documents to both the House and Senate panels in June.

Flynn has not spoken to the congressional committees and has refused requests to appear voluntarily.

Warnings before Trump took office

Flynn’s legal issues stem from foreign payments he received after he started his own consulting firm.

Flynn founded the Flynn Intel Group after he retired from the military in 2014. The Obama White House pushed him out of his role as head of the Defense Intelligence Agency (DIA), the military’s intelligence arm. Flynn was fired over claims he was a poor manager, though he says he was ousted by Obama administration officials unwilling to listen to his warnings about the rise of ISIS and an increasingly aggressive Iran.

Before he was named national security adviser, the FBI began investigating Flynn for secretly working during the presidential campaign as an unregistered lobbyist for Turkey, an investigation he disclosed to the Trump transition team before Trump took office.

Federal investigators were probing whether Flynn was secretly paid by the Turkish government as part of its public campaign against Fethullah Gulen, a critic of Turkish President Recep Tayyip Erdogan who lives in exile in Pennsylvania. Erdogan blames Gulen and his supporters for plotting the failed Turkish coup last summer.

As part of his pro-Turkey lobbying, Flynn and his colleague held meetings during the Trump transition with Turkish representatives. According to The Wall Street Journal, Flynn and his son were offered as much as $15 million to forcibly remove from the United States a Turkish cleric wanted by Turkey.

The alleged plan would directly violate the US criminal code and could carry a punishment of as much as 20 years in federal prison. Lawyers for Flynn said the allegations “ranging from kidnapping to bribery” are completely false.

Flynn’s lobbying firm was paid $530,000 by Inovo BV, a company owned by Turkish businessman Ekim Alptekin, during the final months of the US presidential campaign. The Flynn Intel Group, which is no longer active, was tasked with producing an anti-Gulen documentary, though the final product never surfaced. Flynn also penned an op-ed criticizing Gulen, which was published on Election Day.

In March, Flynn’s firm retroactively registered as a foreign agent that lobbied for the Turkish government.

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(©2017 CBS Broadcasting Inc. All Rights Reserved. CNN contributed to this report.)