Did Jack the Ripper kill only five people?

Answer 1

The experts at the time judged that the mode of operation indicated that the same man had committed all the murders. The wounds were similer. The method was similer. The type of victim was similer.

Answer 2

Jack The Ripper sent letters to the police and press. Scotland Yard felt that a few of the letters were genuine, confirmed more or less by a letter with 1/2 of a human kidney in advanced stages of Brights Disease. The piece of kidney was sent to a Dr. Openshaw for examination. Two weeks later the infamous Dr. Openshaw letter arrived at the pathology division of London Hospital. The kidney was thought to be from Ripper victim Katherine Eddows who was in the last stages of Brights.

This and other letters that could be matched up with the crimes linked the author of the letters to the killer that called himself Jack The Ripper.

Answer 3

Five were proven, although some stories credit him with up to eleven

In a probability no. Although most people believe that Mary Ann Nichols (aka:Polly) was the Ripper's first victim most experts say no. There were at least 2 murders that fit the profile as being Ripper murders. A prositute was found murdered in March of 1888 and another by the name of Martha Tabram was found murdered just weeks before Nichols. And although after the murder of Mary Jane Kelly the murders continued for years the publicity surrounding them was almost non-existant. The police knew about the later crimes but without the publicity and no arrest ever made this led to the idea that Jack the Ripper had stopped.