The Black Dahlia is a pseudonym given to Elizabeth Short, a woman who was brutally murdered in Los Angeles in 1947. This name was used in place of Short's real name as part of the news media's tendency at that time to give florid nicknames to murders that were especially appalling.
Short's murder was indeed shocking. She was an attractive aspiring actress living in Los Angeles who's nickname was inspired by her black hair and her tendency to dress in all black clothing. Her body was discovered severed at the waist and emptied of blood, and other parts of her body, which had been washed before it was dumped, had been mutilated by cutting. News reporting of the crime was particularly lurid, sometimes telling outright lies in order to make the details of the crime more shocking to readers. Due to the notorious nature of the murder, hundreds people have claimed to have taken part in the murder over the years.