On: FBI wants public help solving encrypted notes from murder mystery

[jcl]

I would guess that he is using "E" as a separator, since it seems to occur at almost all end-of-lines and before punctuation/numbers. And maybe the letter just before "E" has some significance, as there is only a small set of letters that appears there, with "SE" extremely frequent. It's possible that he is stripping out vowels as a kind of shorthand.

[extension → jcl]

Indeed, if you examine the scanned notes, there are subtle gaps after most of the "E"s

[noahc → jcl]

I wonder if he might be using a gendered language. Which would explain a high level of xE or even yxE at the end of sentences.

[Shibalba → noahc]

think of it like this miles is mlse to him...he writes as tho he is exhaling at the end of each word. MKSE = makes

[rabbimagus → jcl]

The most common letters in Hungarian are e and a