Very little information regarding the defendant in the murder trial is provided in Rose's script. There are periodic references to him, but little in the way of descriptive information. What can be deduced, however, is that the defendant is a teenage male, 19-years old [Juror #8: "He's nineteen years old."], and is an ethnic minority [again, in the film, he is described as being of Hispanic descent], something derived from the racist comments directed against him by Juror #10. He is poor, and has a criminal record involving theft and violence involving a knife -- the same type of weapon used in the murder of his father. He is made more sympathetic by the description of his father provided in the script as having been in prison with a history of violence, and by repeated references to him as "boy," as distinct from man. In addition, he is described by Juror #8 as follows: "Look, this boy's been kicked around all his life. You know, living in a slum, his mother dead since he was nine. That's not a very good start." Clearly, this information is intended to humanize the defendant and to cast doubt on the notion of him as having committed a premeditated murder, the crime for which he is being tried.
Beyond that, Rose provides no information on the defendant.
Whether the description that can be derived from the bits and pieces of information provided in the play is "accurate" cannot be determined. The characters in "Twelve Angry Men" all existed inside
Rose's head. It is a work of fiction, although inspired by the writer's real-life experience serving on a jury. There is, consequently, no basis upon which to judge accuracy.