"You don't believe in the detective police ?" he said.
"Who _can_ believe in them, who reads his newspaper and remembers what he reads ?" his friend rejoined.

"Fortunately for the detective department, the public in general forgets what it reads.

Go to your club, and look at the criminal history of our own time, recorded in the newspapers.

Every crime is more or less a mystery.

You will see that the mysteries which the police discover are, almost without exception, mysteries made penetrable by the commonest capacity, through the extraordinary stupidity exhibited in the means taken to hide the crime.