The city was on edge, rife with racial tension and awash in conspiracies. Many patrol officers saw themselves as targets in a plot by black residents to kill them. Some New Yorkers who embraced the Black Panther Party’s identity as a political and self-defense group saw the police as an instrument of governmental oppression.

For a long time, Mr. Bell asserted his innocence and, with his co-defendants, sought a new trial on the basis of uncovered evidence showing the first trial was unfair. Mr. Washington died in prison in April 2000. Mr. Bottom, also known as Jalil Abdul Muntaqim, is at the Sullivan Correctional Facility in Fallsburg, N.Y., officials said.

In a statement condemning the decision, Commissioner James P. O’Neill recalled how Mr. Bell and his co-conspirators “shot Officer Piagentini 22 times, including with his own service revolver — as the dying officer pleaded for his own life.”

“Over the past 47 years, he has never expressed genuine remorse,” Mr. O’Neill said.

In a letter the parole board sent to Mr. Bell this week, however, they credited him with finally taking responsibility “for your actions” and expressing “regret and remorse for your crimes.” Noting this maturation, the board quoted back to Mr. Bell what he told panelists during their interview of him on March 3: “There was nothing political about the act, as much as I thought at the time,” Mr. Bell told them. “It was murder and horribly wrong.”

The board undertook a deep review of several factors, including Mr. Bell’s age, scant disciplinary history in prison and his success in compiling a “sturdy network of supporters,” including the Prisoner Reentry Institute at John Jay College of Criminal Justice. In the end, a majority of panelists found that the state had prepared Mr. Bell well for release. Though his crime “represents one of the most supreme assaults against society,” Mr. Bell is capable of living a “law-abiding life,” it wrote.

“On some basic level this is what parole is for,” said Michael Jacobsen, the executive director of the CUNY Institute for State and Local Governance and a former commissioner of the city’s Department of Correction.