This was in use in British press circles some years ago , before e-mail , electronic compositing and newspaper websites with rolling news came along .
If a “source” had a piece of “confidential” news he wanted “leaked” into the public domain , it would be arranged that the incriminating document would be dropped at the chosen newspaper’s main office at [supposedly] midnight - time enough for the splash to make the later editions , but not early enough that the rival newspapers could pick up on it and run it .