A former NYPD transit cop has been ordered back to prison for fatally shooting a man during a 1996 off-duty fight in the parking lot of a Westchester deli.

An appeals court unanimously overturned a 2008 ruling that freed Richard DiGuglielmo and instead reinstated his murder conviction.

He had been released on grounds that prosecutors had covered up evidence that the victim, Charles Campbell, was about to use a bat to bash the cop’s father, who owned the Dobbs Ferry deli.

“There was time to display the handgun and deliver a warning,” the four-judge panel wrote.

DiGuglielmo has served 11 years of his 20-year sentence.