The jury has the ultimate power to decide whether a person is guilty of a crime. It has always been a part of our judicial system. When jurors nullify a law by acquitting a defendant who has obviously broken that law, judges and prosecutors can do nothing about it. A jury's not guilty verdict is final. Defendants often go to trial without having anyone testify for them.
Defense attorneys rely on a variety of arguments to discredit the prosecutor's witnesses.
Prosecution witnesses are mistaken in their observations because the lighting was bad, they were under the influence of drugs or alcohol or they were too far away. Evidence from police laboratories is unreliable because the machines were not properly maintained or the technicians were not properly trained. What these arguments have in common is that they do not depend on defense evidence. Rather, they rely on the presumption of innocence and prosecutor's failure to overcome it by proving guilt beyond a reasonable doubt. I am confused about why a defendant would choose to not testify.