The Peeping Tom is Fan Yu's father‽ Chen Ge never would have imagined that if he had not read the paper notes. Looks like I was right. Fan Yu's aunt has been hiding something crucial from me.
When Chen Ge was trying to deduce the killer earlier, he had been missing a crucial element, a motive. The notes had provided him with a new line of enquiry.
There are three notes, and they have different handwriting. This means that at least three people knew about Teacher Fan's dirty secret. Chen Ge did not touch the notes inside the book. The paper was fragile from the passage of time, and he was afraid that his touch might ruin the key evidence.
