So if they are shamelessly using any means available to try to convict everyone they prosecute, say to increase their rate of successful prosecutions and thus p

So if they are shamelessly using any means available to try to convict everyone they prosecute, say to increase their rate of successful prosecutions and thus professional status, then by your definition then they aren't gunning for anyone? I'd say in that case they would be gunning for everyone they prosecute. As opposed to the people they aren't prosecuting. An alien invader could be gunning for everyone on Earth. "Gunning for" doesn't have some distribution defined definition when enacted by a single individual - an individual can "gun for" everyone in context and some do.