Just thought of something quite ridiculous. The Exorcist film was directed by William Friedkin and adapted for screenplay by William Peter Blatty. Two Williams. The Exorcist Letter features tit willow, ie; Will. Bit of a stretch I know. Here is the last verse of The Mikado’s Tit Willow. I have highlighted the relevant part in bold letters
Now I feel just as sure as I’m sure that MY NAME
ISn’t Willow, titwillow, titwillow,
That ’twas blighted affection that made him exclaim
"Oh, willow, titwillow, titwillow!"
And if you remain callous and obdurate, I
Shall perish as he did, and you will know why,
Though I probably shall not exclaim as I die,
"Oh, willow, titwillow, titwillow!"
It reads MY NAME IS, like the intro to the 13 Symbol Cipher or My Name is..letter. Well William Blatty fits perfectly into the 13 Symbol Cipher with the correct amount of relevant letters.
I need to exorcise this nonsense from my brain.

Signed yours truley Will

Then he plunged himself into the billowy.

And yes I do know the Exorcist movie was released in 1973, two years after the 13 Symbol Cipher. The Novel 1971.

But he did the novel Twinkle, Twinkle, "Killer" Kane in 1966, and Kane is present in the 13 Symbol Cipher.

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