Also, the reason so many related charges are being brought up is that in other, similar cases, many police officers get off on technicalities because the exact charge cannot be proven. It means that the prosecutor feels that the officers could be proven at fault of one or some of these charges, and it's the best way to get something to stick.
The racial makeup of Baltimore is too tied to class to make a straight racial distinction in this particular case. It gets drawn into the larger narrative, of course, because race and economics are so aligned in America, but the crux of the protests in this particular issue is that Baltimore's police is horribly managed and corrupt, from all reports.
As was pointed out before, many of the industrial cities like Baltimore/Detroit/etc. in the U.S., that were building a middle class based on industry specifically barred black people from buying property in up and coming suburban neighborhoods until the end of the 20th century, forcing them to basically rent in the inner city and creating large inner city ghettos when the industry and money base left the cities (and inner city education, public services, etc. dropped along with this as well). Thus, while most of the negative incidents in Baltimore focus on black people, it's also because the entire inner city is basically poor and black - and aligns directly with socioeconomic issues.
The officers being black has absolutely nothing to do with anything, no matter what the case is, anyway. When people say that police unfairly target and punish black people, they are talking about the institution of the police in America, and are not making a distinction between the race of the officers in question.