You had missing letters and they got more frequent as the story progresses. To the point that maybe a 6-letter word became just 3 letters and near the end, a sentence just composed of one letter: w.
Could it be possible you coded something in the missing letters? Maybe the mystery could be solved that way and we'll finally know who the killer is.
Really? Maybe I should proofread this again to see if there's some characters missing. Thanks for the heads up!
I thought they were deliberate mistakes that readers will solve (I feel too lazy to crack code right though).