Adding to this
Well likeSpoiler for this?He had motive & access. Chris' name was scrawled all over the inside of her notebook, so she was obviously into him. But he worked downstairs from her apartment and would have been able to see her coming and going with a variety of people. That's when he went psycho. He also had access to her apartment via the back stairs and an easy excuse to be there (delivering food). He would want to disguise his name in her notebook to prevent suspicion from falling on him. Since he was dating her & probably often took her food orders, he'd know what drink she'd order.
The symbols are actually the laetters of Chris just a pairing of both the lower case and capital version of the letter (for example C and c).
Furthermore, Chris really doesn't seem upset that his recent now ex girlfriend is dead.
I think her cup was poisoned. The killer used ethonal as a solvent, but ethonal has a strong taste. In order to avoid adding too much directly to the drink and risking the taste or smell giving it away the killer added the solution to an empty cup and dumped out the solution leaving enough traces to still be effective. Being ever so careful the killer also wiped down the cups rim which got the solution on it from dumping it out as to avoid a queer taste if she drank from the cup directly. This explains the napkin as very little would be needed to clean the cup rim.
Last but not least, I would hazard that the poison was dissolved in a bottle of rice cooking wine. So long as the bottle wasn't in a place the cook would use it this would serve as an ideal container. Any Asian resteraunt is likely to have numerous bottles of the stuff so the police wouldnt have reason to search them, it would explain the ethonal and last but not least it ties in with my theory of how and why the poison was administered as it was as rice cooking wines can have a very strong very distinct flavour.
Correct on the first part.
Altering symbols drawn all over two weeks worth of notes would have taken a non-trivial amount of time, and if you wanted to mask a five letter name, why change all the same letters the same one, keeping it obvious whatever it was was five letters?
It makes much more sense that the girl drew them herself as some kind of artsy doodling, which was later confirmed by police evidence
Very clever on the second part, you should write your own mysteries! ;D
Also, the napkin was not creased.
But I think you're getting close .