As a historian I do believe that our only chance to find Jack the Ripper is the sources from the past. These sources must be produced by the killer himself. Otherwise they can not be connected to the murders.
What I think we have to do is to find and understand the sources produced by a murderer who is communicating with people. This is very difficult, since some sources from 1888 are lost and since our understanding is biased by post modern thinking. Nevertheless I think it is the only way forward.
The sources must not be in written form. The important thing is that they are greetings from the past.
"The overall conclusions drawn add to our current knowledge base on serial murderers. Gibson (2004) finds that a “consistent compulsion to communicate characterizes these serial killers” (p. 209). In most cases, communicating with society and law enforcement was imperative for the selected killers examined. In their communications they left clues, taunted and insulted law enforcement, re-injured victims’ loved ones, threatened to kill again, made demands and offered explanations for their behavior (see pp. 210-211). A brief comparative analysis suggests that each killer had different motives to communicate (e.g. a form of venting). In fact, “it is what they disclose about themselves that reveals a greater reality” (quoting Joel Norris (1988), p. 212)." http://www.ccja-acjp.ca/en/cjcr100/cjcr167.html
He's certainly got me confused, and not for the first time I may add! Mind you, if the "sources must not be in written form" I guess that rules out the Goulston Street graffiti. Which brings me to another question: Pierre, given your latest reasoning, why did you start a thread on the aforementioned graffiti?