Dude should have told Yamada's indeed super cool when modelling and that's why he bought the magazine she was starring in.
Aside from that, isn't the manga already postponing the first murder too much? The MC isn't even seemingly planning it. We don't even know whom he's going to murder. The author is stretching it a bit too much. After all, that's what this manga is all about, so while I understand the need to introduce all the characters properly, you still can't avoid the main plot for too long.