A massive manhunt is underway in Mercer County after an off-duty Sheriff?s officer was gunned down while trying to break up a domestic dispute in a pizza shop parking lot Sunday.

Police say Josh Hahn, 29, was shot the parking lot around noon. He underwent surgery in Trenton for a chest wound that punctured his lung.

Police say Hahn was shot in front of his father. The two were running errands when police say Hahn saw a fight between a young man and woman in the parking lot. When he pulled in to stop it, police say the man pulled out a gun and fired once to Hahn?s upper torso.

Police are on the look out for the shooter. Law enforcement agencies all over Mercer County are assisting in the investigation, as are the FBI and state police. Residents are urged to contact the Hamilton Township Police Department if they have information.