Why did juror 9 changed his vote twelve angry men?
The 9th among the 12 Juror's is an old Man whose matured & impressive memory, the role played by Jack Warden decides to change his vote, because of the sane reasoning as put forth by the 7th Juror, played by Henry Fonda in support of the accused as not-guilty. Juror 9 changed his vote in favor of Juror 7 because of his stand which would put an 18 year old boy on Death Row by an unanimous decision of the 12 Jurors if voted guilty.
Therefore as a worldly-wise & keen observer of the proceedings in the Court, he weighs the pros & cons, deciding to vote in support of the accuse as not guilty, turning the vote count to 2 not-guilty against the majority 10 Jurors voting him guilty. There are several remakes, but the story & the characters r the same but with different actors. My Answer is based on Sidney Lumet's directorial debut with "12Angry Men" released in 1957. This Courtroom drama was adapted from a teleplay of the same name by Reginald Rose who co-produced and wrote the screenplay for the movie.