(Reuters) - Here is a timeline of significant developments in Special Counsel Robert Mueller’s investigation into Russia’s role in the 2016 U.S. presidential election and contacts between President Donald Trump’s campaign and Moscow.

2017

May 17 - U.S. Deputy Attorney General Rod Rosenstein appoints former FBI Director Mueller as a special counsel to investigate Russian meddling in the 2016 election and to look into any links and/or coordination between the Russian government and people associated with Republican Trump’s campaign. The appointment follows Trump’s firing of FBI Director James Comey on May 9. Days later, Trump attributed the dismissal to “this Russia thing.”

June 15 - Mueller is investigating Trump for possible obstruction of justice, the Washington Post reports.

Oct. 30 - Veteran Republican political operative and former Trump campaign chairman Paul Manafort, who worked for the campaign for five pivotal months in 2016, is indicted on charges of conspiracy against the United States and money laundering, as is his business partner Rick Gates, who also worked for Trump’s campaign.

- Former Trump campaign adviser George Papadopoulos pleads guilty to a charge of lying to the FBI about his contacts with Russian officials.

Dec. 1 - Michael Flynn, Trump’s first national security adviser who also had a prominent campaign role, pleads guilty to the charge of lying to the FBI about his discussions in 2016 with the Russian ambassador to Washington.

2018

Feb. 16 - Mueller secures an indictment of 13 Russian individuals and three firms, including a Russian government propaganda arm called the Internet Research Agency, accusing them of tampering in the presidential race to support Trump and disparage Democratic candidate Hillary Clinton. The accused “had a strategic goal to sow discord in the U.S. political system, including the 2016 U.S. presidential election” according to the court document filed by Mueller.

- An American, Richard Pinedo, pleads guilty to identity fraud for selling bank account numbers after being accused by prosecutors of helping Russians launder money, buy Facebook ads and pay for campaign rally supplies. Pinedo was not associated with the Trump campaign.

Feb. 22 - Manafort and Gates are charged with financial crimes, including bank fraud, in Virginia.

Feb. 23 - Gates pleads guilty to conspiracy against the United States and lying to investigators. He agrees to cooperate and testify against Manafort at trial.

April 3 - Alex van der Zwaan, the Dutch son-in-law of one of Russia’s richest men, is sentenced to 30 days in prison and fined $20,000 for lying to Mueller’s investigators, becoming the first person sentenced in the probe.

April 9 - FBI agents raid home, hotel room and office of Trump’s personal lawyer and self-described “fixer” Michael Cohen.

April 12 - Rosenstein tells Trump that he is not a target in Mueller’s probe.

April 19 - Former New York Mayor Rudy Giuliani, a Trump supporter in the election campaign, joins Trump’s personal legal team.

June 8 - Mueller charges a Russian-Ukrainian man, Konstantin Kilimnik, a Manafort business partner whom prosecutors say had ties to Russian intelligence, with witness tampering.

July 13 - Federal grand jury indicts 12 Russian military intelligence officers on charges of hacking Democratic Party computer networks in 2016 and staged releases of documents. Russia, which denies interfering in the election, says there is no evidence that the 12 are linked to spying or hacking.

July 16 - In Helsinki after the first summit between Trump and Russian President Vladimir Putin, Trump publicly contradicts U.S. intelligence agencies that concluded Moscow had interfered in the 2016 election with a campaign of hacking and propaganda. Trump touts Putin’s “extremely strong and powerful” denial of meddling. He calls the Mueller inquiry a “rigged witch hunt” on Twitter.

Aug. 21 - A trial jury in Virginia finds Manafort guilty of five counts of tax fraud, two counts of bank fraud and one count of failure to disclose a foreign bank account.

- Cohen, in a case brought by U.S. prosecutors in New York, pleads guilty to tax fraud and campaign finance law violations. Cohen is subsequently interviewed by Mueller’s team.

Aug. 31 - Samuel Patten, an American business partner of Kilimnik, pleads guilty to unregistered lobbying for pro-Kremlin political party in Ukraine.

Sept. 14 - Manafort pleads guilty to two conspiracy counts and signs a cooperation agreement with Mueller’s prosecutors.

Nov. 8 - U.S. Attorney General Jeff Sessions resigns at Trump’s request. He had recused himself from overseeing the Mueller inquiry because of his contacts with the Russian ambassador as a Trump campaign official. Trump appoints Sessions’ chief of staff Matthew Whitaker, a critic of the Mueller probe, as acting attorney general.

Nov. 20 - Giuliani says Trump submitted written answers to questions from Mueller, as the president avoids a face-to-face interview with the special counsel.

Nov. 27-28 - Prosecutors say Manafort breached his plea deal by lying to investigators, which Manafort denies. Trump says he has not ruled out granting Manafort a presidential pardon.

Nov. 28 - Giuliani says Trump told investigators he was not aware ahead of time of a meeting in Trump Tower in New York between several campaign officials and Russians in June 2016.

Nov. 29 - Cohen pleads guilty in the Mueller investigation to lying to Congress about the length of discussions in 2016 on plans to build a Trump Tower in Moscow. “I made these misstatements to be consistent with individual 1’s political messaging and out of loyalty to individual 1,” says Cohen, who previously identified “individual 1” as Trump. The president criticizes Cohen as a liar and “weak person.”

Dec. 12 - Two developments highlight growing political and legal risks for Trump: Cohen is sentenced to three years in prison for crimes including orchestrating hush payments to women in violation of campaign laws before the election; American Media Inc, publisher of National Enquirer tabloid, strikes a deal to avoid charges over its role in one of two hush payments. The publisher admits that the payment was aimed at influencing the 2016 election, contradicting Trump’s statements.

2019

Jan. 25 - Longtime Trump associate and self-proclaimed political “dirty trickster” Roger Stone is charged and arrested at his home in Florida. Stone is accused of lying to Congress about statements suggesting he may have had advance knowledge of plans by Wikileaks to release Democratic Party campaign emails that U.S. officials say were stolen by Russia.

Feb. 14 - The Senate votes to confirm William Barr, Trump’s nominee to replace Sessions, as attorney general. Barr assumes broad authority over how much of the Mueller report to release.

Feb. 22 - Manhattan district attorney’s office is pursuing New York state criminal charges against Manafort whether or not he receives a pardon from Trump on federal crimes. Trump cannot issue pardons for state convictions.

Feb. 27 - Cohen tells U.S. House Oversight Committee Trump is a “racist,” a “con man” and a “cheat” who knew in advance about a release of emails by WikiLeaks in 2016 aimed at hurting rival Clinton. Trump directed negotiations for a real estate project in Moscow during the campaign even as he publicly said he had no business interests in Russia, Cohen testifies.

March 7 - Manafort is sentenced in the Virginia case to almost four years in prison. The judge also ordered Manafort to pay a fine of $50,000 and restitution of just over $24 million.

March 13 - Manafort is sentenced to about 3-1/2 more years in prison in the Washington case, bringing his total prison sentence in the two special counsel cases to 7-1/2 years.

- Shortly after his sentencing in Washington, the Manhattan district attorney announces a separate indictment charging Manafort with residential mortgage fraud and other New York state crimes, which unlike the federal charges cannot be erased by a presidential pardon.

March 22 - Mueller submits his confidential report on the findings of his investigation to U.S. Attorney General William Barr.

March 24 - Barr releases a summary of the “principal conclusions” of Mueller’s report and wrote that the investigation did not establish that members of Trump’s election campaign conspired with Russia. Mueller did not exonerate Trump on obstruction of justice, said Barr, who himself concluded the inquiry had not found sufficient evidence to warrant criminal obstruction charges against Trump.

March 25 - Democratic lawmakers demand that Barr send the full Mueller report and any underlying documents to Congress by April 2 and say the attorney general’s summary is not sufficient. The deadline is not met.

April 3 - The Democratic-led House of Representatives Judiciary Committee voted to enable its chairman, Jerrold Nadler, to subpoena the Justice Department to obtain Mueller’s unredacted report and all underlying evidence as well as documents and testimony from five former Trump aides.

April 18 - This date is announced by the Justice Department for the release of a redacted version of the Mueller report.