Baltimore's streets are quiet again. Baltimore's state's attorney Marilyn J. Mosby moved quickly in securing indictments against six police officers in the death of Freddie Gray, and her decisive action has calmed the city for now. 

But getting a grand jury to indict police officers is a lot easier than getting convictions at trial. 

That's because like any prosecutor trying to hold cops accountable, Mosby will be working on an uneven playing field. 

To prove her case, she won't just need sufficient evidence.