I knew a child from the Dallas area because her Dad was a client. I watched her grow up. She grew up large, a young lady almost 6 feet tall. Her dream was to be a sheriff's deputy.
When she graduated from high school and police academy, I personally talked my local sheriff into interviewing her. She was hired on the spot, pending her psychological exam, which went well.
About 4 months later, she was given the option to resign or be fired. She resigned, left town, but is eligible to work in law enforcement anywhere in Texas, and might be, for all I know.
What she did was beat up a prisoner who didn't walk fast enough from Point A to Point B in our jail. She described the prisoner as a smart ass who just should have obeyed the rules, and that she would just go somewhere else and get hired.
This young woman said she bashed the prisoner's head up against the wall a few times, to get her attention.
Thinking back, I recall that her psychological exam was, to her, humorous. She went to see the local doctor, a primary care doctor, with no credentials in mental health. He had a contract with the county to ask questions on a 2 page questionnaire, sign off on whether the subject was mentally ok or not.
On the day she showed up, he was busy doing routine school physicals for high school football players. He asked her to state her name, her address, said to her, "You look sane to me", and signed off that she was psychologically fit for service. It took a couple of minutes.
I suggest we are not screening people well enough, among all the other shortcomings of our law enforcement system.