Is there any kind of CLEAR consensus about what and when the FIRST letter was? Received either by the police or the Central News (etc.)? While there are probably many unprecedented aspects of the case, I'm not aware of letters from a murderer in other 19th century crimes. So I would imagine that the first would be of "primary" importance, and have the highest likelihood of being authentic.
I know in the Lindburgh kidnapping, the first letter, obviously found on the window sill, is considered authentic, but a lot of doubt has come to be placed on the others, including the "boad Nelly" one. Mickey Rosner, Vitale and Spitz, as well as NY gangster Owney Madden, were all curiously given copies by Lindburgh of the first, and the others may have stemmed from an extortion plot developed in the underworld, and not related to the actual kidnapping.
I think the closest modern similarity is the Zodiac killer, who enclosed a piece of cloth from the slain cab driver in one of the letters, developed a sophisticated cipher with which to taunt the police, and a malevolent nom-de-plume. And, of curse, he was never caught either.
And some, like the Torso killings in Cleveland in the 30's, just went about their grim business without the need to unburden their soul.......
You make some good points about the murders. The only message from the killer might have been the murders themselves.
That and there not being any murders during October gives credence to the likelihood that the killer did crap himself due to all the publicity, as that month was the height of the Ripper scare. I think the lapse between Eddowes' murder and Kelly's (and the extent of the latter's mutilation) is partly due to the Ripper being too chickensh*t to have ripped another prostitute up that month and that he was frustrated at not being able to do so.
Boss and the postcard are real. He is going to do a double murder, and wants everyone to know that both are his. If he says nothing, with the speed that he works, there is going to be a high probability that a second killer will come into play, if he waits to claim, the message will be called a hoax. He has few options, the best being what happened here. Send a letter detailing a crime, then include more details of future criminal activity that involves the postal system. By law, the postal system has to be told of any criminal activity that will pass through them, and the special investigation branch will act with the police to monitor the situation. He covered all the bases; he asked for info not to be released, he gave his name, he detailed shipping body parts through the postal system, and he said that he would write again. To make it even easier, he sent the second reply on a postcard. This postcard should have never made it past sorting, and I am not so sure that it did. This postcard is not only suppose to be caught by the post office for coming from someone bent on missusing the postal system, but it is evidence in a crime that has London on the world stage; there should have been chaos in the postal system, no matter when it was spotted,that it made it to the News Agency, but there wasn't, there was just words over the postmark being a day late. The only people that can debate the actual fact of that postcard being delivered, are the same people that are hinted at being the ones that created a possible hoax. Someone cries foul on that postmark, there would be enough evidence, and enough support to end up hanged for someones crimes, and no news is worth death and the condemnation. That postmark would have been just a quick fix, because now they have messed with Jacks plan. I am going to take a wild guess, and say that a message, unlike the first sent for the sake of the double murder, arrived from Jack. With his anger, his confidence, he probably hand delivered it to the police station himself. The..."I think I wet myself" letter. They could not claim a third, it would detail the postmark error, but within the page he would probably express his disappointment, say that he had one more lady to work on, and that he would need time to calm down from what must have been an error concerning his double event. The last, he would write, wouldbe slightly more sweet than the rest, be sure to have all the facts corrects. Pictures and all, they made sure that Mary was well documented, and correct.