The Historic UK website publishes interesting facts about England, Scotland, Ireland, etc. on a day-to-day basis.  Today's entry reads:

27 September 1888:  First use of the name Jack the Ripper in an anonymous letter to the Central News Agency 


This, of course, marked a turning point for the public's perceptions of the killer as well as how the police and newspapers handled the story.  The public had a name for their boogeyman, and the police now saw people accused of being the Ripper just for using the name in conversation.  The fact that the Ripper letter was sent to a news aggregate service rather than a specific newspaper always struck me as fishy, and points to the letter (and all subsequent missives) as being hoaxes.