A prosecutors duty is to prove the guilt of the defendant beyond a reasonable doubt. If the scientific tools are available there is absolutely no reason that they should not be expected to use them to prove their case. Numerous studies have shown that eye-witness testimony is spotty and barely reliable and heavy reliance on it in the past (and today) has led to the convictions of a countless number of innocent individuals. I would rather see a guilty party go free due to lack of forensic evidence than see an innocent go to jail under the same circumstances. If liberty is denied to even one individual who does not deserve it the system has failed.