I do think that there may be some explanation for police brutality to be found in the personality types frequently drawn to police work...but, having observed police close up for a lot of my professional life, I tend to think a lot of their behaviour may be attributed to unresolved extreme trauma.
They are recruited almost as children and are rapidly exposed to horrific accidents, appalling domestic situations (eg they are the people who turn up at the frontline of horrible child abuse cases, DV,), awful crime scenes etc.
They see the worst of humanity before their brains are fully formed, often in situations where they fear for their lives.
Perfect recipe for ptsd
To add to this, in general they work in non trauma informed organisations which prize apparent imperviousness to the horrors they experience and punish normal human responses and sensitivity.
They also tend to become isolated from normal responses in that their work and experiences mean they tend to cling together socially with a somewhat fortress mentality.
They quickly learn....as all of us in frontline jobs where we deal daily with extremes of human experience do...that nobody wants to know about what you do except others doing it. Also, people in these jobs generally don't want to contaminate their family lives with horror.
It's a recipe for appalling behaviour or suicide...which happens a lot with cops.