FARGO, N.D. (AP) — A former federal prosecutor who handled such prominent cases as the 1977 trial of Native American activist Leonard Peltier has died.

Lynn Crooks died on Sunday, the North Dakota U.S. Attorney’s Office said. He was 83.

Crooks was an assistant U.S. attorney from 1969 to 2002, and led the prosecution team at Peltier’s trial in Fargo, KFGO reported. Peltier was convicted in connection with the shooting deaths of two FBI agents in 1975 on the Pine Ridge Reservation in South Dakota. He was sentenced to life in prison and was recently denied parole.

Crooks also prosecuted Yorie Kahl and Scott Faul in connection with a fatal shootout in 1983 near Medina, North Dakota, that left two federal marshals dead. Kahl was the son of Gordon Kahl, who was part of the anti-government Posse Comitatus group and also was involved in the shootout.

Crooks served in various roles during his career, including as first assistant U.S. Attorney and acting U.S. attorney. In 2000, he told The Associated Press that his calling was to be a federal prosecutor.

“If I had the opportunity to go back and change it all, I wouldn’t change a thing,” Crooks said then. “I don’t think there’s any better job a lawyer could have.”

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In 2016, he supported a ballot initiative that added crime victim rights to North Dakota’s state constitution.

North Dakota U.S. Attorney Mac Schneider issued a statement Monday praising Crooks.

“While North Dakota will remember Lynn for prosecuting challenging and consequential federal cases of national prominence, his colleagues will remember him as a kind and generous man who was never too busy to help a friend or mentor a young attorney,” Schneider said.

He also lauded Crooks as “arguably the greatest prosecutor in the history of North Dakota.”