In an English village, you turn over a stone and have no idea what will crawl out.
Miss Marple

Then there are some minor points that strike me as suggestive - for instance, the position of Mrs. Hubbard's sponge bag, the name of Mrs. Armstrong's mother, the detective methods of Mr. Hardman, the suggestion of Mr. MacQueen that Ratchett himself destroyed the charred note we found, Princess Dragomiroff's Christian name, and a grease spot on a Hungarian passport.

It often seems to me that's all detective work is, wiping out your false starts and beginning again."

"Yes, it is very true, that. And it is just what some people will not do. They conceive a certain theory, and everything has to fit into that theory. If one little fact will not fit it, they throw it aside. But it is always the facts that will not fit in that are significant.

When you read the account of a murder - or, say, a fiction story based on murder - you usually begin with the murder itself. That's all wrong. The murder begins a long time beforehand. A murder is the culmination of a lot of different circumstances, all converging at a given moment at a given point. People are brought into it from different parts of the globe and for unforeseen reasons. [...] The murder itself is the end of the story. It's Zero Hour.”

He paused.

“It's Zero Hour now.

One little Indian left all alone, he went out and hanged himself and then there were none.

Why didn't they ask the Evans?