I agree with the premise that American soldiers are taught and display a more rigid rules of engagement abroad but I would be interested to see exactly what kind of ex-soldier becomes a police officer.

My suspicion is that the kinds of soldiers who become problem police officers are the soldiers who didn't actually face combat abroad. I imagine it's the kind of soldier who fantasized about front-line service but wasn't quite cut out for it for one reason or another and they've directed their disappointment about that into being an abusive police officer.

Generally, the kinds of cops that become whistleblowers, or are fired for insufficient brutality, are veterans.

The archetypical "warrior cop" is a non-veteran who likes military imagery but has no experience with military discipline or subordination.

Actually yea - I can't deny that your proposed person is pretty likely to go into policing after serving in the military. But I do think that people with a strong sense of civil service would also be likely to follow that path, people (generally speaking) aren't going into the military for glory - a lot of folks do it out of civil obligation and another large slice is there since it's a good way to get some economic mobility.

That said, yea, glory hounds would make really scary police officers.

Rules of engagement depend on where you are, who you're fighting and who is watching. Turns out that the US doesn't enforce any RoE in its borders, and you can use all the brutality and shiny weapons that you want against people living there with little to no oversight at all.