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US District Court Judge Mark L. Wolf, who served as chief judge of the federal district court in Boston before taking senior status in 2012, has fully retired from the bench, officials said Friday. In a statement, Clerk of Court Robert M. Ferrell’s office said Wolf, appointed by Ronald Reagan to the court in 1985, was stepping aside “after more than 40 years of service to the public” as a federal jurist. “Judge Wolf has served on this Court with distinction for over four decades,” Chief Judge Denise J. Casper of the federal district court in Boston said in the statement. Wolf’s “steadfast commitment to the rule of law, determination in wrestling with novel issues of fact and law, and dedication to making fair, equitable, and legally sound decisions without fear or favor are the hallmarks of his time on the bench,” Casper said. Wolf, 78, famously held several hearings during the 1990s that revealed the FBI’s corrupt relationship with informants Stephen “The Rifleman” Flemmi and James “Whitey” Bulger. The exposure instigated investigations within the FBI and Justice Department that led to obstruction of justice and racketeering charges against ex-FBI agent John Connolly. Advertisement In addition, Wolf oversaw Mafia trials that included the prosecution of legendary New England boss Raymond Patriarca Jr. and reduced a prison sentence for Mafia member Vincent Ferrara following wrongdoing by prosecutors. In 2003, Wolf became the first judge in more than 50 years to sentence a defendant to death in Massachusetts, in the trial of serial killer Gary Lee Sampson. Sampson was convicted of killing 69-year-old Philip McCloskey of Taunton and 19-year-old Jonathan Rizzo of Kingston after they picked him up hitchhiking. Eight years after the Sampson sentence, Wolf sentenced former House Speaker Salvatore F. DiMasi to eight years in prison following his conviction on corruption charges. Wolf said he hoped DiMasi’s sentence would put a stop to Beacon Hill’s “culture of arrogance.” Advertisement In 2012, Wolf sentenced a hacker convicted of helping people steal internet access to three years in prison. The hacker, Ryan Harris, earned between $400,000 to $1 million for facilitating the theft of Internet access from cable companies. That same year, he approved a deal that created an alternative to disciplinary segregation for prisoners with severe mental illness following a series of inmate suicides in segregation units in state prisons. Also in 2012, Wolf ruled in a controversial decision that the state must pay for convicted murderer Michelle Kosilek’s sex change operation. Kosilek, formerly known as Robert Kosilek, strangled her wife to death in 1990. “His many opinions on complex issues of law in notable cases have had a great impact on jurisprudence,” Casper said Friday. “In addition, his tenure as Chief Judge led to the increased engagement with the bar and community. ... I, along with my colleagues and this court community, applaud his years of dedicated service.” Prior to his judicial appointment, the statement said, Wolf was a lawyer for the Justice Department and also worked as an attorney in private practice. Material from prior Globe stories was used in this report. Travis Andersen can be reached at travis.andersen@globe.com.