The job of the prosecutor (at whatever level) is to get to the truth of the matter. The elected prosecutor is under pressure to get a conviction and in more than a few cases those convictions or lack of convictions translate into votes or lack of votes. Prosecutors when running for office often times list their convictions as accomplishments.
This troubles me. Why? It all goes to the heart of justice. Justice is not determined by a ballot box or a poll, but by truth. The prosecutor is very open to being pressured into convicting anyone just to obtain the conviction. Fail to convict a suspect in a sensational murder and the career of that prosecutor may flatten due to failure to win reelection. So, the prosecutor may feel pressure to obtain a conviction regardless of the truth of the matter.
Now, do not get me wrong. I do not believe most prosecutors to be corrupt. I do not see them in their offices plotting their reelection over a trail of wrongful convictions, but the pressure may contribute to being more eager to believe things supporting wrongful conviction than things supporting the suspect's innocence.
Yes, the lacrosse rape case is driving this post, but I recall thinking about this five years ago in regards to the death penalty. The DNA testing came back and did not finger the suspects, still the prosecutor is continuing his investigation. Now, there may be a whole lot of other evidence indicating there is a valid case against those players but I have a hard time imagining it. After all, we have a guy here in Wisconsin who was let go on a rape conviction based on 18 year old DNA evidence.