The Adventures of Philip Marlowe
The Adventures of Philip Marlowe was a radio detective drama that aired from 1947 through 1951, based on the character from the Raymond Chandler novels. The L.A. detective was mostly played by Gerald Mohr, although Van Heflin starred in the 1947 run.
This is classic hard-boiled detective action, with each episode starting with the words: "Get this and get it straight. Crime is a sucker's road and those who travel it end up in the gutter, the prison, or the grave." No witty remarks from charming detectives in this show!
You can find more episodes in the Ear Benders section.
Here is a sample of the online episodes currently available at The Old Time Radio Fan: