On July 22, 168 years ago, Thomas Lynch was the first police officer in America (at least best I can tell) to be fatally injured in the line of duty:
Patrolman Lynch responded to 16 Dover street after receive a report of a large dispute. As he tried to mediate the dispute, he was struck in the head 11 times with an iron pipe. He was seriously injured and died 14 months later from his injuries.
Keep mind the the New York Municipal Police Department was the only municipal American police department for four years. (In the 1850s most cities set up similar organizations.)
I wanna read whatever comes out of this research you've been doing.