In most cases, jurors go into a case looking for reasons to convict. In police misconduct cases, they are searching for reasons to acquit. 175 Prosecutors, therefore, are hesitant to bring cases against police officers that are difficult to win, while one reason for the difficulty in successfully prosecuting officers may be the rarity of such efforts, causing jurors to disbelieve allegations of criminal activity that differ from their typical image of police officers. District attorneys count on officers' testimony to support their cases during trials of alleged criminals. In some jurisdictions, district attorneys are elected and are aware that the powerful police unions and their supporters may withdraw their support if a police officer is prosecuted.
Prosecutors are also aware of juries' tendency to support the police.
Even with apparently foolproof cases against police officers, juries have often been reluctant to find officers guilty of criminal conduct, particularly when the incident occurred while they were on duty. Because cases against police officers are usually difficult to win, prosecutors contend that it is best to pursue only the cases with the greatest chances of conviction. Of course, by only pursuing rare, overwhelmingly strong cases, the deterrent effect of criminal prosecution of officers is undermined significantly. Prosecutors contend that trying, and losing, a case against an officer is a worse signal to send to officers, and the affected communities, than not trying the case at all. For this reason, her office will pursue only exceptionally strong cases.