The actor in question? Jimmy Stewart, one of the most legendary of Hollywood's legendary actors. And the film? Call Northside 777, a pseudo-noir about a cynical, stubborn newspaper reporter who refuses to settle for legend over fact.
The film also features the legendary scenery-chewing Lee J. Cobb, who should probably have been in every noir or semi-noir or pseudo-noir ever made. (Or every movie ever, even). Oh, and it's on NETFLIX INSTANT, so give it a whirl.
An intrepid journalist is persuaded by a mother desperate to free her imprisoned son to investigate his decade-old conviction for killing a policeman.