That's going to be a tough one. The role of the defendant in 12 Angry Men is uncredited; as I understand it, even the fact that the actor is really "John Savoca" is uncertain, as there are no primary sources that mention his last name.
FWIW, the Social Security Death Index says a man named John Savoca who
was born on 29 February 1940 and got his Social Security card in New
York died on 29 June 2005. They only have seven John Savocas in their
database, and this is the only one who'd have been the right age in
1957. He could still be alive, of course.