Indigenous activist Leonard Peltier, who has spent most of his life in prison since his conviction in the 1975 killings of two FBI agents in South Dakota, has been denied parole.

The U.S. Parole Commission said in a statement Tuesday announcing the decision that he won't be eligible for another parole hearing until June 2026.

His attorney, Kevin Sharp, a former federal judge, argued that Peltier was wrongly convicted and said that the health of the 79-year-old was failing.

The FBI and its current and former agents dispute the claims of innocence.

An enrolled member of the Turtle Mountain Chippewa tribe, Peltier was active in the American Indian Movement, which began in the 1960s as a local organization in Minneapolis that grappled with issues of police brutality and discrimination against Native Americans. It quickly became a national force.

AIM grabbed headlines in 1973 when it took over the village of Wounded Knee on the Pine Ridge reservation, leading to a 71-day standoff with federal agents. Tensions between AIM and the government remained high for years.

On June 26, 1975, agents came to Pine Ridge to serve arrest warrants amid battles over Native treaty rights and self-determination.

After being injured in a shootout, agents Jack Coler and Ronald Williams were shot in the head at close range, according to a letter from FBI Director Christopher Wray. Also killed in the shootout was AIM member Joseph Stuntz. The Justice Department concluded that a law enforcement sniper killed Stuntz.

Two other AIM members, Robert Robideau and Dino Butler, were acquitted of killing Coler and Williams.

After fleeing to Canada and being extradited to the United States, Peltier was convicted of two counts of first-degree murder and sentenced in 1977 to life in prison, despite defense claims that evidence against him had been falsified.