Native American activist Leonard Peltier was defiant toward the government but grateful to his family and supporters as they welcomed him home to North Dakota, one day after his release from a Florida prison where he had been serving a life sentence in the 1975 killings of two FBI agents.

Mr. Peltier’s murder conviction and two life sentences, stemming from a 1975 shootout with F.B.I. agents on a reservation, have been widely criticized.

Peltier, who has always maintained his innocence in the killing of two FBI agents 50 years ago, was released Tuesday from a federal prison in Florida.