I'm familiar with the program to get military equipment. Much of our old entry team was supplied through this program. We had humvees we got from the military.
There are solutions to the problems, and they aren't that bad.
Yearly qualifications. Regular reassignments, and incidental qualifications are a start. Psychological retesting would be advisable in bigger city areas and large metro areas. And a civilian auditor being hired.
Take a civilian auditor, make them either an auditor or give them inspector status with arrest authority, and have them regularly conduct and review things. If they're there to be outside of the rank and file then you won't have the issue of things slipping through the cracks.
As soon as I saw the tape, I knew it wouldn't take long before the public would see more complaints existed. By Saturday morning the news caught wind of the additional previous complaints. A civilian investigator in a city would have reviewed, been paid to see those for what they are, and flagged those guys.