Says Wikipedia:

The stories followed a formula in which a person's criminal acts were typically undone either by an overlooked but important detail or by their own stupidity. On rare occasions a curious twist of fate caused the story to end happily for the episode's protagonist. Ironic twist endings were a key feature of each episode. The Whistler himself narrated, often commenting directly upon the action in the manner of a Greek chorus, taunting the criminal from an omniscient perspective.

How did he know all these things? Well, he walked by night. I guess that’s all it took. He walked by night, and hence knew many things. He knew the thoughts they dare not speak. A guy can learn a lot with a stroll after dark, I guess.

He was just a way of getting into the story and pushing it along; he didn’t interfere. But the voice - taunting, as the description said, and sly and amused - made it different from any other mystery story. Unlike “Inner Sanctum,” the tales didn’t rely on supernatural elements; unlike “The Mysterious Traveller,” which used the same format, the stores weren’t predictable. You always knew who was guilty. You didn’t know how it would end.

End it did, with a double thump on a timpani.

Fans of the show are used to three things: Marvin Miller’s introductions, the unvarying sponsorship of Signal Gasoline (your go-farther gasoline) and the theme, which is not exactly the easiest thing to whistle. (I can, though. Really.) If you pay attention in "The Two Jakes," you'll hear the song coming from a car radio.

It only ran on the West Coast. Kids who grew up in LA had a media experience the kids in Brooklyn didn’t. Imagine that. It’s like not being able to access a YouTube video because you’re in another country.

You can find a vast quantity of Whistlers here, for free.