In his 129-page ruling, U.S. District Judge Kurt Engelhardt called for a federal investigation of the former prosecutors, saying they had committed "grotesque" misconduct during the officers' trials, The (New Orleans) Times-Picayune reported.
Former officers Kenneth Brown, Robert Gisevius, Robert Faulcon, Anthony Villavaso and Arthur Kaufman were convicted in 2011 for their roles in the September 2005 shootings on the Danziger Bridge following Hurricane Katrina in which two people died and four other people were wounded, all of whom were unarmed.
The five officers petitioned for a new trial last year, alleging prosecutorial misconduct.
Engelhardt accused Sal Perricone and Jan Mann, former U.S. prosecutors, of committing "unprecedented events and acts" that had taken the court "on a legal odyssey unlike any other."
The judge said the evidence he reviewed in granting the new trials "illustrates the diseased root that unfortunately casts an ineradicable taint on these convictions."