I believe the letter has “nice” misspelled which leads credulence to the immigrant, and less to either Queen Victoria’s Doctor or grandson.
I also thought it could be the immigrant with that who, “Jewes” writing on the wall, red herring or not.
Not really. The writer has no problem with "fried", "piece", "signed". "While" and "knife" are mispelled, but as the unexpected "whil" and "knif".
There are other mispellings which appear to be Stage Irish "sor" "prasarved".
But correct the mispellings and add punctuation, the letter becomes formal Business English.
Survey says hoax by medical students.
An ethnic German was also a suspect; and for that matter, there are over 600 letters purporting to be from Jack the Ripper, and not all of them are, and it’s also possible that none of them are.
If DB Cooper can’t be identified, and that was merely 40 years ago...