(CNN) Herman Bell is a three-time cop killer -- and that's all that matters to those angry over the New York Board of Parole's decision to release the 70-year-old.

To his supporters, Bell is a model for how a repentant, rehabilitated prisoner can return to society. Too often, they say, incarceration favors revenge over rehabilitation, and Bell's release suggests that may be changing.

Bell walked out of the maximum-security Shawangunk Correctional Facility in upstate New York on Friday, following the parole board's March decision to grant his eighth bid for parole. Bell will live in Brooklyn, where he will be supervised for life, according to the state Department of Corrections and Community Supervision.

At least three organizations will assist Bell in transitioning back into society, the parole board said. Bell agreed to get a job, submit to drug tests, stay away from bars and nightclubs, abide by a curfew and participate in a mental health evaluation and anti-violence counseling.

Bell, a Black Liberation Army radical at the time, was convicted in the fatal 1971 ambushshootings of NYPD Officers Waverly Jones, 33, and Joseph Piagentini, 28. He pleaded guilty to voluntary manslaughter in the 1971 killing of San Francisco police Sgt. John Young.

Bell served 46 years in prison for the killings of Officers Joseph Piagentini, left, and Waverly Jones.

In outlining its decision, the parole board cited Bell's age, his 46 years in confinement, his relatively clean prison record, his maturity and remorse for the crimes, a strong network of supporters and the board's belief that Bell "can live a law-abiding life." His "incarcerated debt has been paid to society," the panel ruled.

The decision was not unanimous. While board members Otis Cruse and Carol Shapiro voted in favor of his release, Caryne Demosthenes dissented, according to a parole document.

Infuriated, the president of the New York City Patrolmen's Benevolent Association pilloried the board. The union, which says it has received 367,000 letters opposing Bell's release , is demanding legislative action to close loopholes it says allow the board to set cop killers free.

"The parole board has lost their god****** humanity to think that a murderer should walk their streets. I don't want a murderer in my damned neighborhood, nor do you," PBA President Pat Lynch said at a Friday news conference.

Diane Piagentini, the widow of one of the slain New York officers, excoriated Gov. Andrew Cuomo, who appointed the board members.

"Shame on you," she wrote. "You should have put politics aside and done the right thing. You should have given us a new parole hearing."

Gov. Andrew Cuomo is under fire but says he doesn't agree with the decision to free Bell.

His office would renew his offer to meet with Piagentini's widow. Cuomo said in a statement to CNN affiliate WCBS that he disagreed with the parole board's decision but noted the board is wholly independent.His office would renew his offer to meet with Piagentini's widow.

Scores of legal and civil rights groups issued a joint statement applauding Bell's release as an example of "transformational criminal justice reform."

"This decision is the right outcome in this case based on the criteria used to determine parole," the statement said. "We must not allow politics to undermine the rule of law, nor should we discourage an agency from correctly performing its duties by allowing it to be bullied or cowed by the loudest voices and those with their own agendas."

The Office of the Appellate Defender, an indigent defense group, also lauded the decision.

"If rehabilitation is a goal of incarceration, we should applaud the parole board's decision to release a person whose institutional record warrants it," said managing attorney Lisa Packard

The killings

Bell was a member of the Black Liberation Army, a militant offshoot of the Black Panthers that engaged in robberies, bombings, prison breaks and attacks on police in California's Bay Area and other locales in the 1970s.

At the time, the Bay Area was a hotbed of oft-violent anti-government demonstrations and black nationalism, and groups like the BLA and Weather Underground regularly attacked police and other government entities. The BLA was particularly active in San Francisco and New York. The New York State Fraternal Order of Police estimates the BLA killed at least 10 police officers during the era

Police were relentless in targeting such revolutionary outfits. At a national level, the FBI had for years been tapping its Counter Intelligence Program, or COINTELPRO , to disrupt domestic political organizations it deemed too radical.

On May 21, 1971, Bell and two other BLA members, Albert Washington and Anthony Bottom, ambushed NYPD Officers Waverly Jones and Joseph Piagentini as they responded to a call in north Harlem, according to the parole board's letter outlining its decision.

Herman Bell's supporters say he is a reformed man who made the most of his life in prison.

In opposing Bell's bid for parole, city police Commissioner James P. O'Neill said in March that the men made a phony 911 call solely to lure the officers into an ambush.

After Jones and Piagentini responded to the Colonial Park Houses complex, Bottom shot Jones in the head, back, neck and buttocks with a .45-caliber handgun, killing him instantly, according to a New York Police Department report titled "The Truth About Herman Bell."

"Bell's killing of Piagentini was cruelly prolonged," the report said, explaining that as the officer begged for his life and told the men of his daughters, 1 and 3 at the time, Bell unloaded his weapon into Piagentini before taking the officer's own gun and shooting him again.

"After Bottom robbed Jones of his gun, (Bottom) finished off Piagentini," the report said.

Various reports say Piagentini was shot 22 times. The officers' slayings would inspire a book and made-for-TV movie, "Badge of the Assassin."

Following the killings in Harlem, Bell, Washington and Bottom returned to San Francisco, where Bottom and Washington attempted to kill a police sergeant with a machine gun, according to the NYPD report. The gun jammed, the men were arrested and Bell led a raid the next day on the Ingleside precinct, where he killed Sgt. John Young with a shotgun, the report said.

Arrest and trial

Bell was arrested in New Orleans the following year, and the shotgun used to kill Young was among five guns found in his apartment, the NYPD said.

According to reports in The New York Times, prosecutors initially tried five members of the Black Liberation Army. A week after a defense lawyer for one of the men complained the prosecution's case was full of inconsistencies and that the charges were based on "coercion, threats and psychological torture," a mistrial was declared in May 1974, The Times reported.

"Several jurors (were) said to have refused to believe evidence or witnesses or trust police," the paper reported in 1974.

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A second trial focused only on Bell, Washington and Bottom, and in April 1975, prosecutors secured their convictions, the paper said.

According to the NYPD report, witnesses identified Bell, his palm print was found at the scene and Piagentini's gun was found near a Mississippi property belonging to his family.

Bell was sentenced to 25 years to life in prison. Bottom, who received the same sentence, has a parole hearing slated for June. Washington died in prison in 2000.

In 2007, Bell appeared before a California judge and, according to the parole board letter, received a sentence of one year in prison and five years of probation after pleading guilty to voluntary manslaughter in Young's slaying.

The terms of the deal dictated that Bell would not testify against any other defendants, and his plea deal could not be used as evidence in other cases, the San Francisco Chronicle reported at the time

Clean record?

Bell was not a model prisoner at first, according to the NYPD report. While on trial, he overpowered a Rikers Island prison guard and took the guard's keys before being subdued, the report said.

After Bell and his codefendants were sentenced in May 1975, officers conducting a courthouse search discovered the men had been smuggled lock-picking tools, knives and explosives, according to the NYPD report and an article in The New York Times.

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The parole board letter does not mention either incident. Rather, it said that Bell committed six infractions in prison, only three of which would be considered Tier 3, or severe: a 1995 demonstration for which he was put in solitary; a 2000 instance of "unauthorized organization," which is not explained; and a 2017 "unhygienic act," also not explained.

"Said history as examined against the length of your incarceration, the years between each infraction is indicative of an overall satisfactory adjustment to your lengthy incarceration," the board's letter stated.

In 2017, Bell was accused of assaulting staff, according to the parole board, but there is no detail of the allegation. Instead, the board's report said Bell was pepper sprayed and suffered a concussion and fractured ribs at the hands of prison staff.

Bell was experiencing short-term memory loss and having difficulty speaking at the time of the board's letter, which concluded, "The disciplinary history available at the time of the interview did not indicate an infraction related to this incident, therefore received no consideration."

Is Bell remorseful?

The board also cited in its letter Bell's regard "for the pain and suffering (he) caused the family of the victims." He has expressed remorse and asked forgiveness, the letter said.

Board members were particularly moved by a statement they said demonstrated "maturation and insight" and marked a reversal to Bell's previous claims of being a political prisoner.

"There was nothing political about the act, as much I thought at the time," Bell said. "It was murder and horribly wrong. ... It was horrible, something that I did, and feel great remorse for having done it."

The NYPD report takes issue with the board's conclusion that Bell is sorry for what he did.

"Until 2010, Bell maintained his militant posture, denying everything except the righteousness of his cause," the report said. "In his 2012 hearing, he no longer denies killing the officers, but he remains tight-lipped and sketchy on the details of the crime that left Joseph Piagentini bleeding from twenty-two wounds."

State Sen. Martin Golden and other lawmakers urge the parole board to reverse its decision last month.

Bell emphasized the racial and social upheaval of the 1970s, telling the parole board, "We received a tremendous amount of repression from the state, so we had no choice but to respond," according to the NYPD report.

In his 2014 parole hearing, Bell said he had long ago quit rationalizing the officers' killings.

"The consequences of what I had done came to the surface and I learned from being in prison what it's like to be separated from loved ones," he is quoted as saying in the NYPD report.

In 2016, he took more responsibility for the crimes and insisted he was a good person. On more than one occasion, he said his actions in 1971 were a response to police aggression in the community, the report said.

"I'm not a bad person, that I was caught up in a situation that in the process of trying to do good, I did something very terribly wrong, that I did something bad, and that, you know, my activities wasn't focused on their loved ones per se," he is quoted as saying.

The parole board said Bell's change of heart and his "institutional adjustment" were factors in granting him parole.

Backlash

At least one of the victims' family members supports Bell's release. Jones' son's name is redacted from the parole board letter, but several media outlets have attributed a February statement to him:

"The simple answer is it would bring joy and peace as we have already forgiven Herman Bell publicly. On the other hand, to deny him parole again would cause us pain as we are reminded of the painful episode each time he appears before the board."

Bell attorney Robert Boyle confirmed in a news conference that Waverly Jones Jr. was OK with Bell being paroled.

"In these times of increased hate, we need more compassion and forgiveness," Boyle quoted Jones Jr. as saying.

Media reports indicate Jones' brother, Manny Jones, was not as magnanimous. He told the New York Daily News , "I was having nightmares of this guy getting out of prison. It's just wrong."

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A second chance for Bell isn't a notion that sits well with many lawmakers in the state, New York Mayor Bill de Blasio among them. He said in a letter to the parole board's chairwoman , "Murdering a police officer in cold blood is a crime beyond the frontiers of rehabilitation or redemption."

The mayor further said he worried that the ruling sends a dangerous message to law enforcement, a sentiment echoed by Piagentini's widow, who has served more than 20 years with the US Marshals Service.

"The message being sent devalues the life of my brave husband who was taken from his two daughters and for whom there is no parole," she said in a statement . "How can we ask our police officers to risk their lives to protect society when society fails to appropriately punish their animalistic killers?"

The final paragraph in the NYPD report also expresses concerns about what freeing Bell might mean to police.

"Herman Bell is a liar and a three-time killer, a terrorist who has refused to renounce terrorism in any way that matters," it said.

"The message to police officers in New York, San Francisco, and throughout the country is also painfully clear: Your sacrifices can and will be forgotten. Herman Bell should remain in prison until the end of his days. His mind has not changed, his heart has not opened, and his debt has not been paid."