It was reported today that the local PD there does not require psychological screening, which if done right is a reliable and tested way to weed out undesirable characters. For a few hudred dollars a candidate, this could very likely have been avoided. It's not a new idea either. I did police candidate screenings for quite awhile back in the 80's and 90's and caught some real psychopaths who would otherwise have been hired and issued a badge and a gun.
While screening might be improved, no one is responsible here except the shooter.
Mental evaluation of anyone in this type of position should be a mandatory annual and random requirement. No difference than annual and random blood and drug tests.