Over the years, criminal justice system has evolved in different ways. The most important has been in the area of forensic investigation where different techniques has been used to gather, analyzed and present evidence in court. Evolution in forensic science has lead to accuracy in evidence. The most important areas of forensic science has been evolution of DNA testing which has provided a more accurate way testing evidence and thereby incriminating or exonerating the suspect. DNA plays a critical role in criminal justice system by providing concrete evidence that can be proved beyond reasonable shadow of doubts in a criminal case. DNA provides criminal investigators with first hand technique that use unique body features to analyze evidence collected form the scene of crimes. Although it has been criticized because it cannot stand on its own in criminal prosecution, it always collaborate other evidence and therefore plays an important role in criminal cases. The uniqueness of DNA over other forensic techniques is because it relies on body features like fingerprint patter ns, blood type, and others which are unique to every individual. This means the chances of giving wrong conviction is highlight reduced. Although it has its disadvantages, DNA testing provides one of the most reliable evidence in criminal cases.