Yup, I heard in this audio lecture:
http://ebook30.com/audiobooks/audiob...eir-world.html
( and I don't have any reason to doubt the lecturer ) that when they were making a movie based on The Big Sleep, in working over the scenario they found out they can't determine who murdered the chauffeur from the book. So they wired Chandler asking him that. And he wired back "I haven't the slightest idea".