Justice Department appointed Robert S. Mueller III, a former FBI director Wednesday as special counsel to oversee the investigation into alleged connections between President Donald Trump’s campaign and Russian officials. The 72-year-old attorney has a long history with investigations and public service.

Mueller served as FBI director before James Comey who was fired by Trump last week. The decision to name Mueller as special counsel came after a huge turmoil in administration since last week after sudden dismissal of Comey. It also followed subsequent disclosure that Trump asked former FBI director to discontinue the investigation of his former National Security Officer Michael T. Flynn who had alleged ties with Russian officials.

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Deputy Attorney General Rod J. Rosenstein released a statement upon the appointment of special counsel, which said: “It is in the public interest for me to exercise my authorities and appoint a special counsel to assume responsibility for this matter.

“My decision is not a finding that crimes have been committed or that any prosecution is warranted. I have made no such determination,” Rosenstein added.

Trump also released a statement following the appointment and emphasized on his earlier claims that the allegations were false and his campaign had no ties with a foreign entity.

His statement read: “ As I have stated many times, a thorough investigation will confirm what we already know — there was no collusion between my campaign and any foreign entity. I look forward to this matter concluding quickly. ”

Special counsel is a position that can be used under a statute which permits the attorney general or a deputy in the absence of an attorney general or if he recuses himself to conduct an independent investigation. A special counsel has been called upon once earlier during Bill Clinton administration when former Senator John Danforth was appointed to investigate Branch Davidian siege outside Waco, Texas. A special counsel is not similar to an independent counsel.

Mueller was appointed as FBI director by George W. Bush and served in the position for 12 years. He also served former President Barack Obama’s administration for a long time. He oversaw the FBI from Sept. 4, 2001, till Sept. 4, 2013.

“I accept this responsibility and will discharge it to the best of my ability,” Mueller said in a statement Wednesday, according to the Guardian.

He had been the FBI director for just a week when the 9/11 attacks took place in September 2001.

"You talk about a learning curve," Art Cummings, former executive assistant director for the National Security Branch of FBI, told TIME in May 2011 in a cover story on Mueller. "He's barely been on the job, hasn't met many of his senior executives" and suddenly is faced with "the 'oh, crap' moments," Cummings said further.

His 12-year term can be characterized by various significant and turbulent times including the agency's deadly confrontation with Branch Davidians in Waco, Texas, the discovery of FBI agent-turned-Russian-spy Robert Hanssen and disclosure of documents withheld from lawyers representing convicted Oklahoma City bomber Timothy McVeigh, most of which he dealt with successfully.

Even after leaving FBI in 2013, Mueller did not restrain himself from high-profile investigations.

In 2015, Mueller conducted an investigation into the NFL's handling of a video of former running back Ray Rice who was accused of punching his then-fiancee. In 2016, he was asked by Booz Allen Hamilton to investigate a security review after a contractor was arrested for allegedly stealing national security secrets.

Philip Mudd, a CNN contributor and former deputy director of the FBI's national security branch who worked under Mueller, praised his appointment to CNN's Wolf Blitzer on his show.

"Every American who thinks that this is a moment of turmoil, whether they like the President or not, should breathe easy tonight: Robert Muller is solid ground," Mudd said.

"He is not one of the best, Robert Mueller, he is the best I ever saw. Leadership, judgment, decision-making," he added. "There is nobody better at doggedly pursuing a target without being subjected to any pressures from Congress, the President, the media, anybody in the FBI, the attorney general, the deputy attorney general. There is nobody better," he further said.

Mueller graduated from Princeton University in 1966 and later joined Marine Corps. He served as an officer for three years and acquired a Purple Heart along with a Bronze Star, two Navy Commendation Medals and the Vietnamese Cross of Gallantry, according to his FBI biography.

Mueller’s appointment was praised by several lawmakers who called it a “positive development” and said that it means that the investigation into alleged ties between Russia and Trump’s campaign will go on as it should.