At the end of Act I in Twelve Angry Men, which juror changes his vote to "not guilty" and why?

It is Juror Nine, the elderly man on the jury, who changes his vote from guilty to not guilty at the end of Act One, and he is the first juror to do so. Juror Nine changes his vote to support Juror Eight, who wants to discuss the evidence before reaching a verdict. Juror Nine says he wants to hear more, also. By the end of the play, Juror Nine has played a significant role in sifting through the facts of the case to reach a fair verdict.