The murderer was carrying an umbrella--and an open umbrella--have you the piece of silk?
If so, let us look at it." The superintendent produced the square inch of silk from his waistcoat pocket, and examined it closely: "Of course it's umbrella silk," he exclaimed, slapping his leg.

"Funny I didn't recognise it at the time." "Perhaps I wouldn't have recognised it myself, but for the fact that a piece of umbrella silk formed an important clue in a recent case I was engaged upon," replied the detective.

"Experience counts for a lot--sometimes.

See, this piece of silk is hemmed on the edge--pretty conclusive proof that the murderer was carrying the umbrella open, to shield him from the rain, and that it caught on the nail outside the window, tearing off the edge.

He closed it as he got inside the window, and placed it near the window-sill, and the rain dripped off it and formed the pool of water.