OF ALL FELONY CASES WHICH ARE PROSECUTED, 85 PERCENT ARE RESOLVED BY A GUILTY PLEA; THE OTHER 15 PERCENT ARE RESOLVED BY A TRIAL OR BY DISMISSAL OF CHARGES. IF A CASE IS DISMISSED, SOMETHING WAS WRONG WITH THE PROSECUTOR'S EVIDENCE. THE DEFENSE ATTORNEY MUST CONCENTRATE ON THE CRIME SCENE IF HE IS GOING TO FIND A HOLE IN THE PROSECUTOR'S CASE. THE PRIMARY ROLE OF THE DEFENSE ATTORNEY IS SEEN AS ONE OF TESTING THE CREDIBILITY OF THE WITNESSES. IF HE CANNOT CHALLENGE A WITNESS'S CREDIBILITY, THEN HE MAY CHALLENGE THE ADMISSIBILITY OF THE EVIDENCE. IF CRIME SCENE INVESTIGATORS MAKE ERRORS OR ARE CARELESS IN PRESERVING EVIDENCE THEY HAVE FOUND, THE DEFENSE ATTORNEY CAN QUESTION THEM, MAKE THEIR TESTIMONY IMPROBABLE, AND CAST DOUBTS ON THEIR CREDIBILITY. ONE TECHNIQUE EMPLOYED BY THE DEFENSE IN QUESTIONING THE PROSECUTION'S EXPERT WITNESS IS THAT OF CALLING AN EQUALLY QUALIFIED EXPERT. THIS EXPERT MAY SAY WHAT TECHNIQUES SHOULD HAVE BEEN USED IN TESTING A PARTICULAR SUBSTANCE OR ITEM. IF THE PROSECUTION'S EXPERT HAS NOT USED THIS PROCEDURE, THE DEFENSE ATTORNEY MAY ASK HIM WHY HE DID NOT AND QUESTION THE EFFECT THE DISCREPANCY MAY HAVE HAD UPON THE FINDINGS, THUS CAUSING THE JURY TO DOUBT HIS TESTIMONY. (VDA)