In uniform so not a private security gig. Also, assume he was armed.
Multiple outlets report the victim was working an off-duty job.
Police departments regularly have officers in uniform while working and being paid by private companies. From the NYPD Paid Detail Unit (PDU): "All Paid Detail police officers are considered off-duty, acting as private contractors... All officers will report in full uniform to the location designated by the vendor for check-in and assignment."
https://www.nyc.gov/html/nypd/downloads/pdf/public_information/nypd-258_paid_details_2016-06-16.pdf