More than 30 Democratic members of the House and Senate are calling upon President Joe Biden to grant executive clemency for a notorious convicted cop killer, according to ABC News.

The subject of the Democratic members' letter to Biden is Leonard Peltier, who was a leader in the American Indian Movement activist group in the 1970s. He was later sentenced to serve two life sentences in 1977 following his conviction for the 1975 shooting deaths of FBI Special Agents Jack Coler and Ronald Williams on a South Dakota reservation.

Democrats highlight allegations of "constitutional violations and prosecutorial misconduct"

Written by Rep. Raul Grijalva (D-AZ) and joined by 32 others, the letter to President Biden raised the "nearly five-decade imprisonment" of Peltier and stated, "Now, more than ever, bedrock principles of justice warrant your consideration of a grant of executive clemency or support of compassionate release at the Federal Bureau of Prisons."

"(N)ow in his 48th year of incarceration," Peltier "is 79 years old and in failing health," the Democrats continued. "Mr. Peltier is serving two life sentences in a maximum-security federal prison for aiding and abetting in a case where his co-defendants were found not guilty on the grounds of self-defense."

The letter went on to cite various "key figures" from Peltier's prosecution -- including a former appeals court judge, a former prosecutor, a former FBI agent, and a United Nations group -- who have since come forward and alleged various "constitutional violations and prosecutorial misconduct that took place during the investigation and trial that led to his conviction."

That includes claims that Peltier was subjected to "anti-Indigenous bias" and has been detained solely because he is a Native American, as well as an "FBI Family vendetta" stemming from the murder of the two FBI agents in 1975.

Biden urged to release "wrongfully imprisoned" convicted cop killer

"As Members of Congress, we sign this letter with a deep commitment to the crucial role we play in upholding justice for all Americans -- and to also hold our government accountable when we see a case of injustice, as demonstrated by the long incarceration of Leonard Peltier," the Democrats wrote. "We stand with the Tribal Nations of the United States, Indigenous voices worldwide, and leading voices on human rights and criminal justice around the globe in support of Mr. Peltier’s release."

"We applaud your commitment to criminal justice reform and your administration’s work to address inequities in the criminal justice system and rectify the past wrongs of our government’s treatment of Native Americans," the letter to President Biden concluded. "We urge you to take the next step by granting Mr. Peltier executive clemency or compassionate release."

In a statement to ABC News, Rep. Grijalva said, "Nearly half a century after he was wrongfully imprisoned, Mr. Peltier's continued incarceration is a grim reminder of this country's long history of stealing life and legacy from Indigenous communities."

"I'm not alone in calling for his clemency -- global civil rights leaders like Nelson Mandela, Mother Theresa, and Archbishop Desmond Tutu have all supported the call as well," the congressman added. "And now we have congressional leaders across the political spectrum and across both chambers asking for the righting of this wrong."

Law enforcement opposition to request for clemency

Of course, not everybody agrees that Peltier should receive clemency, including the National Fraternal Order of Police, which also published a letter to President Biden "to urge you to reject or ignore the most recent requests from misguided activists and Members of Congress to grant any clemency to the convicted cop-killer Leonard Peltier."

Citing the FBI's facts of the case, the NFOP letter said there was "no doubt that Peltier executed" Special Agents Coler and Williams as well as that "found guilty of this heinous crime."

"There should be no doubt that anyone who murders a law enforcement officer in cold blood should be punished to the fullest extent of the law, which means they should serve the full term of imprisonment for which they were sentenced," the letter continued. "This man is one of the most notorious cop killers in our history -- he should not ever be considered for clemency."

The NFOP's letter concluded by noting that former President Barack Obama "made the right call" in rejecting prior pleas for clemency for Peltier, and added, "(W)e have every confidence that you will make the right decision for the families of Special Agents Williams and Coler during the course of your Administration. We believe the calls for his release because of his age and health issues are deeply misguided and unjust."