Depends on how you look at the numbers. But construction, logging, garbage collection and truck driving tend to be the most deadly depending on the specific metric (absolute, per capita, by industry, etc).

Expanding that, the deadliest part of being a police officer is almost certainly the driving component. No gun will save you from smashing your SUV into a pole. And the aftermarket modifications made to the vehicles aren't crash tested. A police cruiser is full of potential projectiles.