Should be noted that in St. Louis County, the Prosecuting Attorney is an administrative post primarily, and that actual cases are normally handled by lower-level prosecutors from the staff.
Here's a quote from a news article:
"As the County Prosecutor, McCulloch can be expected to have input into major decisions about the direction of the case, but it is likely that assistant attorneys will be the ones to handle the day to day matters relating to the grand jury and prosecution. Indeed, McCulloch's spokesman told the St. Louis Post-Dispatch that the grand jury proceedings starting on August 20 will be handled "by the attorney regularly assigned to the grand jury. It will not be handled by Mr. McCulloch."
The decision to indict, to issue a "true bill", rests at this point with the grand jury. If an indictment is issued, then the individual would be booked on whatever charges were returned and a trial date would be set.
The prosecution at trial would be handled by "prosecutors" from the staff.
As many have noted, this would likely be a drawn-out affair. Note that the officer is subject to the possibility of a civil "wrongful death" lawsuit....IF it can be shown that he acted outside the law or outside of his own department's policies and procedures.
If a police officer acts within those restrictions, he is shielded from such prosecution....
However... the department itself is not. In these cases, the lawsuit seeks to prove that the policies and practices of the city itself vis-a-vis it's police department are at fault.
Also... The officer may be the subject of federal prosecution. In order to do this, it must be shown that he violated Brown's civil rights. Normally, they would have to prove that he acted out of racial hatred. (or other civil-rights offenses) A history of proven bigotry would have to be shown.