When did Jack the Ripper become a killer?

Answer 1

Life in London's east end was fraught with violence. So when thirty-five year old prostitute Martha Tabram was found dead with 39 stab wounds and a slit throat, it was hardly news. Even the murder of Mary Ann (Polly) Nichols didn't raise much of a stir. But with the death of Annie Chapman the whole of London was terrified and the whole world was outraged. Jack The Ripper is probably the world's first serial killer that made headlines throughout the entire world. He was big news. The sad thing is, he is still big news. Most likely because he was never caught, it lends a certain mystery to the legend of this notorious killer.

Answer 2

Until there is a definitive answer as to who was the first victim it would only be guessing when he became a killer.