ALBANY - Six former New York state parole commissioners have signed on to an unprecedented amicus brief that accuses the board of caving in to outside pressure to keep behind bars a “cop killer” who long ago paid his debt to society.

The amicus brief in the case of Pablo Costello accompanies a petition alleging that the Board of Parole withered under a media spotlight and pressure from the New York City Patrolmen’s Benevolent Association (PBA) and rescinded parole for an offender who had been approved for release and was within four days of walking out of prison for the first time in more than 30 years.