Boy, once Warner Brothers got their hands on a script, they remade it until the type faded from the page.
"The Man Who Talked Too Much" is a 1940 film that is a remake of a 1932 film, "The Mouthpiece" starring Warren William. I haven't actually seen "The Mouthpiece," and the trivia here says that this script wasn't completed at the time of production, so I'm assuming this is a reworking. In 1955, this movie was remade as "Illegal" starring Edgar G. Robinson, which I saw and liked, with the exception of one plot hole.
The basic story is this: A district attorney, Steven Forbes (George Brent) sends an innocent man to the gas chamber, quits, and becomes a defense attorney. He has a hard time making ends meet until he becomes an attorney for the mob. Once he hits the big time as a mob lawyer, he hires an assistant, Celia, and his brother John. John (William Lundigan) and Celia (Brenda Marshall) fall in love. John is concerned about the honesty of the firm, but his efforts to correct the situation get him into big trouble.
Though the basic premise is the same in each story, in "Illegal," the brother business is changed and the person in trouble is his assistant, played by Nina Foch.
This is an okay story. Despite the holes in "Illegal," I liked it better, Robinson being a stronger actor than George Brent.