Looks to me like it might be a mnemonic text compression scheme, not encrypted text. I've known one person who used pictograms as mnemonic memory aids. I think this man was using the first letter of words as mneumonic aids to each word in his note. Therefore, each letter has a context sensitive meaning that reminded him of the text of his note. However, don't assume he could spell -- he may have heard the wrong sounds for the beginning of words and therefore may misspell even the first letters of a word. While most people get at least the first letter of a word correct, I know a few who that seem to have an auditory equivalent of dyslexia and make mistakes there too.
In that vein, the key will be the numbers and related letters around them, especially the repeated ones. The numbers are likely not encoded since the meaning of the rest of the text is obscure.
For example, "E 71" "E 74" and "E 75" on page 1 might mean Interstate (or "Enterstate") 71, 74 & 75. Then the trailing "NCBE" could mean "nice camping by interstate (enterstate)" or "no collecting by exit" or, well, practically anything. Without knowing a lot more about the man and his life, it would be impossible to even begin to guess.
Final insight. Page 1 is organized and formatted nicely, and appears like it might have been done on lined paper. It is probably a copy of some original notes about things important for him to remember. If this is really a mnemonic compression scheme, then this page will be the rosetta stone. It would be interesting to know whatever became of page(s) 2 and later of his transcribed notes (nobody denotes a page as page 1 unless there's more than one page). The notes page is more haphazard, with groups circled. It was probably the notes he was taking that day, or at least the notes he hadn't spent time to transcribe yet. One of the last notes was probably why he was killed, although its doubtful any of them are notes about killer -- they're probably about something completely unrelated and he was just unfortunate enough to be seen taking notes while looking at something in the wrong direction.
I hope they catch the murderer someday.