If there is a common theme in a set of sources hypothesized as containing descriptions of communications of a serial killer and these different sources of communication is corresponding with the motive(s) of the hypothesized killer, there is significance. But since significance can be illusory, one must research the sources properly.
An example is the theory about Lechmere. The sources that Fisherman has found can be used to establish a significance in the relation between sources and theory. But the risk that the significance is illusory is high, since the sources are not researched properly, i.e. Fisherman uses sources with low reliability.
This must not be a problem per se for the significance, but since he also uses a small set of sources for a wide theory,
i.e. the murderer of Polly Nichols was the murderer of Chapman, Stride, Eddowes and Kelly, he uses the significance to postulate a theory that has nothing more to stand on than one tiny leg (sources with low reliability for only one murder).
So what we must have is a set of sources, connected to more than one murder site and preferably to all of them, which all correspond with the motive(s) of one specific person.
In that way, we avoid making a billion possible interpretations randomly or by our own bias. If the sources are corresponding with the motive(s) and also with the life of someone on a micro level, the significance increases and the risk of low validity and reliability decreases.
What we get then is coherence, and this is something very valuable for writing history. For example, in the case of Lechmere, Fisherman is trying to establish coherence on a micro level. But it is impossible to do so for the rest of the victims, which means that there is almost NO coherence in the theory of Lechmere being Jack the Ripper. Just one tiny part of the theory can stand by itself with the help or newspaper articles who are not reliable. This is how historians establish facts, but in the case of Lechmere, they are poorly established.
Clues From Killers: Serial Murder and Crime Scene Messages
By Dirk C. Gibson. Westport, CT: Praeger, 2004
And also, here are some examples of other serial killers communications with the police. And it could hypothetically give you a picture of what sort of communications I would expect from Jack the Ripper:
The Lipstick Killer of Chicago:
"For heavenís sake, catch me before I kill more; I cannot control myself"
The Zodiac Killer of San Francisco:
"Dear Editor, This is the Zodiac speaking I am back with you."
The BTK killer:
"...How about some name for me, its time: 7 down and many more to go. I like the following. How about you? 'THE B.T.K. STRANGLER', 'WICHITA STRANGLER', 'POETIC STRANGLER'"
The Weepy-voice killer of Minnesota
called the police to say the newspaper accounts of some of the murders were inaccurate.
Happy Face Killer of Oregon:
A message was found scrawled on a wall at the Greyhound Bus Depot in Livingston, Montana: "I killed Tanya Bennett Jan. 21, 1990 in Portland, Oregon. I beat her to death, raped her and loved it. Yes, Iím sick, but I enjoy myself too. People took the blame and Iím free".
The Zodiac Killer of New York:
To The New York Post August 4th 1994: "Hi, Iím back".
By the way, do you see how most of them, in these examples, write about "I" or "me". I find this very, very interesting. You have killers who are making statements about themselves through communications.
Also, the BTK-killer was found through his communication with the police.
"Dennis Rader, otherwise known as the BTK killer, thought he had some sort of understanding with Wichita, Kan., police Lt. Ken Landwehr, head of the multiagency task force that was trying to catch him.
In the weeks before his arrest, Rader had asked po*lice whether he could communicate with them via a floppy disk without being traced to a particular computer.
Police responded by taking out an ad in the classified section of the local newspaper, as Rader had instructed, saying ďRex, it will be OKĒ to communicate via floppy disk.
A few weeks later, such a disk from BTK was sent to a local television station. The disk was quickly traced to Rader through a computer at his church." http://www.abajournal.com/magazine/a...ps_caught_btk/