When the play starts how many of the twelve jurors think the defendant is guilty?
At the start of the play, out of the twelve jurors eleven think that the boy is guilty. Only Juror Eight votes not guilty as he is not entirely convinced that the boy committed the crime by the evidence presented by the prosecution and finds some shortcomings in their arguments to convict the boy.
The Juror does not think that it is right for him to sentence a boy to death until he is absolutely certain that it was the boy who murdered his own father. He wants all the Jurors to discuss the various points put forth by the prosecution and have another look at all the evidence presented to them by the prosecution.