Washington DC - Leonard Peltier has been denied his parole request by the federal Parole Commission after nearly five decades behind bars.

The 79-year-old was convicted in the 1975 killings of two FBI agents on the Pine Ridge Indian Reservation and has been imprisoned for the last 48 years.

Peltier has staunchly maintained his innocence, and his lawyer, Kevin Sharp, warned during his parole hearing earlier this month that this was "probably his last chance," per NBC News.

"Today's announcement continues the injustice of this long ordeal for Leonard Peltier," Sharp said.

"This decision is a missed opportunity for the United States to finally recognize the misconduct of the FBI and send a message to Indian Country regarding the impacts of the federal government's actions and policies of the 1970s."

The Turtle Mountain Band of Chippewa member has also received support from lawmakers over the years, including Brian Schatz of Hawaii, Ed Markey of Massachusetts, and Bernie Sanders of Vermont, all of whom have called for the release of the longest-held political prisoner in the US.

His fight for freedom has also earned support from Nelson Mandela, Pope Francis, and more.

FBI Director Christopher Wray supported the Parole Commission's decision and claimed that "the weight of the evidence has supported his conviction and his life sentence."