The Bento Shop?

I have to be honest here. I watched Suspect X because of Masaharu Fukuyama, the suave Japanese actor-singer who plays the lead character, Professor Manabu Yukawa, who has a penchant for solving bizarre crime cases. However, my fascination with Fukuyama was fleeting in the movie- Suspect X - I was almost instantly drawn into the mindgames of Yukawa and his friend Tetsuya Ishigami, a math genius whom he became acquainted with while studying in university. The clash of two academic geniuses make Suspect X a very engaging and thought-provoking movie to watch. Unlike other whodunit movies, the crime was committed at the start of the movie and we knew the identity of the murderer - Ishigami. What was intriguing for me was to find out how Ishigami committed the murderer(and almost got away with it) and at what point in the movie did Yukawa realize that Ishigami was the murderer. Was it the morning when they walked past the bento shop? Or was it a question Ishigami asked? I’m not going to let the cat out of the bag here. Watch the movie to find
out.