Like if you know some cop was just being a douche bag do you still have to try the case as an associate DA (assistant state attorney in FL)? Do you as an assistant/associate prosecutor have the power to decide what cases you try?
ADA's usually have an oath to serve justice. In theory, they are supposed to adhere to that over winning at all costs. If you know there is exculpatory evidence, you talk to your supervisor and the defense attorney and work to get the charges dismissed. It is highly unethical to do otherwise.
I was in the Criminal Defense Clinic in law school. And I have a couple of friends who were/are prosecutors.