Jack the Ripper
Nobody knows who Jack the Ripper really was. Some think he might have been a doctor or a butcher because of how he killed and cut up the women, much like how a surgeon might perform surgery, or how a butcher might dissect an animal. All the murders happened on weekends, so it could have been someone who did not live in London but visited the city on weekends, or someone who worked during the week and was only free at the weekends.