What was the verdict? Who or what was the main driving force behind the verdict?

The eventual verdict is "not guilty".  The jury is 11 to 1, and 3rd Juror stands alone. At first, he stands firm, saying that he will be the holdout to make this a hung jury. He launches himself into a final massive rant against the boy that descends into nonsense. 8th and 4th Jurors make a short final plea, and 3rd Juror finally concedes, saying “All right. Not guilty.” The Foreman informs the Guard that they have reached a verdict, and the Jurors leave the courtroom.