Ruby,
Baltimore can't get and keep cops because their pay is so low compared to surrounding counties.
Also, the working conditions are extremely dangerous because the poverty is concentrated within the beltway. There's virtually no middle class in the city at all; there's endless poverty and only some lucky working class. There's gangs there. It's a black hole of concentrated crime.
The net effect is that they can't find decent cops who live in the city to hire, and when they do, they can't retain them. Their job is dangerous and, in general, just awful. They see terrible, terrible things and some of them are never the same again.
Cops get their first couple of years' experience in Baltimore city and then transfer to the surrounding counties for both a raise and better working conditions.
This is from personal experience. I just accepted a teaching job there and have lived there in the past. My husband grew up there. The city got more and more dangerous which is why we moved.