How does one identify such a person? Surely this did not happen out of the blue.

Sadists like this, don't just wake up one day and go on a destructive spree.

I'd bet my last dollar, there are clear tell-tale signs in his historical patterns of behaviour.

And for him being an expat, Somebody did not dig deep enough.

Or this guy was a great pretender.

There are always signs....

Employers.... do your due diligence. Avoid taking chances on people with toxic behaviour traits. They never change and it never goes away.