When departments gets desparate for people to fill positions, they'll hire anyone. It's not easy to get someone willing to do a ****** job for ****** pay.
This is probably my favorite quote about law enforcement ever (don't remember the origin):
The chief selling point for professional policing seems to be the idea that sworn government agents are more competent crime solvers than grand juries, private prosecutors, and unpaid volunteers. But this claim disintegrates when the realities of police personnel are considered. In 1998, for example, forty percent of graduating recruits of the Washington, D.C. police academy failed the comprehensive exam required for employment on the force and were described as "practically illiterate" and "borderline-retarded."