Thanks for playing and the feedbacks. During testing, some people found it too complex to solve so I had to tone down the investigation (a lot), basically cutting out most of the red herrings (a few lines still seems out of place since I had to do it quickly).
I am still puzzled about the average difficult and don't have an answer: perhaps a hard version without questions and more things to write at the end?
The suggestions to choose what you want to read is really good, my only doubt is that people will feel overwhelmed by all the documents on the desk right at the beginning.