Former FBI Supervisory Agent Robert Fitzpatrick, who testified on behalf of James “Whitey” Bulger and who claimed to have found the rifle used to kill the Rev. Martin Luther King Jr., has agreed to plead guilty to unspecified charges, according to papers filed Wednesday in US District Court.
The documents do not cite what charges Fitzpatrick will plead guilty to on May 5. He was facing six counts of perjury and six counts of obstruction of justice.
US Attorney Carmen Ortiz’s office last April obtained the indictments against Fitzpatrick, who is the author of “Betrayal, Whitey Bulger and the FBI Agent Who Fought To Bring Him Down,’’ based on his sworn testimony at Bulger’s trial, on July 29 and 30, 2013.
The indictment alleged that since 1998, Fitzpatrick “falsely held himself out as a whistle-blower who tried to end the FBI’s relationship with Bulger,’’ the Globe has reported. Fitzpatrick, who served as assistant special agent in charge in Boston from 1981 to 1986, was Bulger’s key witness during his trial.
Fitzpatrick, 76, testified that he questioned whether Bulger was truly cooperating with the government as an informant and that he was concerned that Bulger was continuing to commit crimes. He said supervisors prevented him from removing Bulger from the informant program.
The indictment alleged, among other issues, that Fitzpatrick lied when he said he had found the rifle used to kill King on the day he was assassinated in 1968, and when he said he had arrested then-New England Mafia underboss Gennaro “Jerry” Angiulo in 1983.
Prosecutors deny Fitzpatrick’s claim that he was one of the law enforcement officials who found the rifle used to murder King, saying he was not there. They also said that despite his claims to the contrary, he never personally arrested Angiulo.
Fitzpatrick’s defense attorney, Robert Goldstein, said Wednesday he could not comment.
A spokeswoman for Ortiz confirmed that Fitzpatrick has agreed to plead guilty, but declined further comment.
The forthcoming guilty plea comes after federal prosecutors said they were willing to search through files at the National Civil Rights Museum in Memphis and the National Archives in Washington, D.C., to prove that Fitzpatrick lied under oath.
Fitzpatrick, who was scheduled to go to trial in June, has previously denied he has lied.
The court papers filed Wednesday were jointly signed by Fitzpatrick’s attorney and federal prosecutors. “The parties have reached agreement in principle to resolve this case,’’ the joint statement said.
Both sides asked a federal judge to set May 5 as the date for Fitzpatrick to enter his guilty plea, and said they would file documents detailing the plea agreement.
Bulger was convicted of charges that he participated in 11 murders, drug trafficking, racketeering, money laundering, extortion, and other crimes.
Bulger fled Boston shortly before his 1995 racketeering indictment. He eluded a manhunt until he was captured in Santa Monica, Calif.
Bulger, 86, is serving a life sentence in federal prison.
Shelley Murphy of the Globe Staff contributed to this report. Milton J. Valencia can be reached at mvalencia@globe.
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@miltonvalencia. John R. Ellement can be reached email@example.com. Follow him on Twitter @JREbosglobe