This is an unsolved mystery about a series of murders that occurred in Austin, Texas in the late 1800s. The victims were all female servants, and the killer was never identified. The case has become known as the "Servant Girl Annihilator" due to the brutality of the murders
From Wikipedia
The Servant Girl Annihilator, also known as the Midnight Assassin, was an unidentified American serial killer who preyed upon the city of Austin, Texas, in 1884 and 1885. The moniker “Servant Girl Annihilator” originated with the writer O. Henry. The series of eight axe murders were referred to by contemporary sources as the Servant Girl Murders.