Prosecutors in most parts of the United States are either in elected positions, or they are interested in someday seeking one, such as a District Judge or the like. So in that way, many, many cases are either pursued or prosecuted with different amounts of zeal because, whatever the legal considerations, the outcome will affect popular opinion and therefore elections.
Take, for example, the trial of Byron De La Beckwith in Mississippi, on two occasions in the 1960s for the murder of civil rights leader Medgar Evars. In one of the trials, the former Governor of the state, Ross Barnett, entered the courtroom, while Evars widow was on the stand, and shook hands with Beckwith in front of the jury. The trial resulted in a hung jury.