It dominated headlines for two years, but in March 2019, special counsel Robert Mueller’s probe into Russian meddling in the 2016 election came to an end. The investigation, which President Donald Trump continually called a “witch hunt,” found no evidence that Trump’s campaign colluded with Russia, but fell short of completely exonerating the president.

FRONTLINE’s The Mueller Investigation draws on interviews with U.S. officials, Trump advisers, legal experts and journalists to give an inside look at the key moments of Mueller’s inquiry, which led to the indictments of more than 30 people. We followed the twists and turns of the investigation. Here’s what we know:

WHAT WAS THE FOCUS OF THE INVESTIGATION?

Mueller’s probe focused on Russian attempts to disrupt the 2016 election; possible coordination between associates of Trump and Russia; and whether financial crimes were committed by any of the president’s associates.

In June 2017, following Trump’s firing of former FBI Director James Comey, the special counsel investigation expanded to examine whether the president had attempted to obstruct justice.

HOW DID MUELLER DO IT?

Mueller obtained thousands of emails from the Trump transition team and interviewed at least two dozen current and former Trump advisers, the president’s Trump’s son-in-law and senior adviser, Jared Kushner; former White House Communications Director Hope Hicks; former Press Secretary Sean Spicer; and former Chief of Staff Reince Priebus. Mueller’s team subpoenaed Trump’s former chief strategist Stephen Bannon to testify before a grand jury, according to The New York Times. Mueller’s team never interviewed the president.

The team consisted of 19 lawyers, who were assisted by 40 FBI agents, intelligence analysts, forensic accountants and other professional staff. The counsel issued more than 2,800 subpoenas and interviewed around 500 witnesses.

WHAT DID THE SPECIAL COUNSEL FIND?

On March 25, Attorney General William Barr sent a summary of what he called the “principal conclusions” of Mueller’s report to key members of Congress. Mueller’s full report has not been made available to the public, though members of both parties have called for its release.

Barr wrote in his summary that the report is divided into two parts: the results of the investigation into Russia’s interference in the 2016 presidential election, and an examination of whether the president obstructed justice.

Barr said that the special counsel “did not find that the Trump campaign or anyone associated with it conspired or coordinated with Russia in its efforts to influence the 2016 U.S. presidential election.” Barr quoted directly from the report: “[T]he investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities.”

According to Barr, the special counsel found two main Russian efforts to meddle in the 2016 election. The first was through the Internet Research Agency, a Russian organization that conducted “disinformation and social media operations in the United States designed to sow social discord, eventually with the aim of interfering with the election.” The second was the Russian government’s hacking operations “designed to gather and disseminate information to influence the election.” The counsel found that government actors in the Russian government successfully accessed emails of people affiliated with the Clinton campaign and Democratic Party organizations.

Barr said that Mueller’s team did not determine whether Trump illegally obstructed justice, writing: “while this report does not conclude that the president committed a crime, it also does not exonerate him.”

In his summary, Barr wrote that he and Deputy Attorney General Rod Rosenstein determined that the special counsel’s investigators did not have enough evidence to prove Trump had obstructed justice.

WAS ANYONE ELSE IMPLICATED IN THE REPORT?

Barr wrote that Mueller’s report did not recommend any further indictments, noting that the indictments and convictions in connection with the investigation had all been publicly disclosed.

Here’s who was indicted in connection with the Mueller investigation:

The Russians: On Feb. 16, 2018 the special counsel indicted 13 Russian nationals and three companies with using fraud and deceit to interfere in the 2016 election, creating hundreds of social media accounts that falsely appeared to be operated by Americans.

On July 13, 2018, the Justice Department announced indictments in Mueller’s investigation against 12 Russian intelligence officers for hacking the Democratic National Committee and Hillary Clinton’s presidential campaign. Prosecutors allege that the individuals targeted over 300 people affiliated with the Clinton campaign, the Democratic National Convention, and the Democratic Congressional Campaign Committee.

Paul Manafort and Rick Gates: On Oct. 30, 2017, Mueller brought charges against Trump’s onetime campaign chairman Paul Manafort and his former business partner Rick Gates on counts related to money laundering, tax evasion and foreign lobbying. Prosecutors alleged that Manafort laundered more than $18 million from income he made while lobbying for a pro-Russia political party in Ukraine.

Gates pleaded guilty to conspiracy and lying to FBI agents and prosecutors on Feb. 23, 2018 and is currently awaiting sentencing. Manafort was convicted on counts of bank and tax fraud in August 2018. He was scheduled to face another criminal trial on other charges from Mueller’s team, but on Sept. 14, 2018, Manafort pleaded guilty to two conspiracy charges as part of a plea deal. He was sentenced to 7.5 years in prison.

Konstantin V. Kilimnik: Konstantin V. Kilimnik was indicted June 8, 2018, on charges of obstructing justice in relation to lobbying efforts to support Viktor F. Yanukovych, a former president of Ukraine. Kilimnik and Manafort tried to convince associates to lie to investigators about the scope of their campaign, prosecutors allege.

George Papadopoulos: The former foreign policy adviser to the Trump campaign pleaded guilty to lying to the FBI. The indictments stemmed from a conversation he had with a professor with alleged connections to the Russian government, who told Papadopoulos that Russians had “dirt” on Hillary Clinton in the form of “thousands of emails.”

On Sept. 7, 2018, Papadopoulos was sentenced to 14 days in prison.

Michael Flynn: Trump’s former national security adviser pleaded guilty in Dec. 1, 2017, to lying to the FBI about his communications with a former Russian ambassador during the presidential transition.

According to court filings, on the same day that former President Barack Obama announced sanctions against Russia for interfering in the election, Flynn called a “senior official” on the presidential transition team to discuss contacting the ambassador about the sanctions.

Flynn cooperated with Mueller under a plea agreement.

Alex van der Zwaan: Alex van der Zwaan pleaded guilty on Feb. 20, 2018 to one charge of making false statements to the FBI. Court documents filed by the special counsel office alleged that van der Zwaan, the son-in-law of one of Russia’s wealthiest men, misrepresented details about his communications with Gates.

On April 3, 2018, Zwaan was sentenced to 30 days in prison and fined $20,000 for lying to investigators.

Richard Pinedo: The Southern California computer science major pleaded guilty to identity fraud on Feb. 12, 2018. Prosecutors said that Pinedo had sold and purchased bank account numbers over the internet, many of them which were created by using stolen American identities.

A spokesperson for the special counsel said that prosecutors had “no evidence and there is no allegation he was a witting participant in the Russian efforts to interfere in U.S. elections and political processes.”

Michael Cohen: President Trump’s former attorney pleaded guilty to lying to Congress about a Trump real estate deal in Moscow he had worked on before the 2016 presidential election. Prosecutors allege that in an August 2017 letter Cohen sent to congressional committees investigating Russian election interference, he falsely stated that the project ended in January 2016. Mueller’s investigators also allege that Cohen falsely stated that he had never agreed to travel to Russia for the real estate deal and that he did not recall any contact with the Russian government about the project. He pleaded guilty Nov. 29, 2018.

Roger Stone: Jan. 25, Roger Stone, a Republican political operative who was an adviser to Trump and an official in the Trump campaign until August 2015, was indicted on seven counts — five counts of making false statements, one of witness tampering and one of obstruction related to his testimony to the House Intelligence Committee about his efforts to find out when WikiLeaks would release more damaging emails about Hillary Clinton’s campaign. The charges state that Stone “corruptly influenced, obstructed, impeded” the House investigation and knowingly made false statements about his interactions with Julian Assange, the head of WikiLeaks. Stone was released on bond later that day.