@Akera93
Wakasa Rumi (the teacher) was obviously sus, but the author portrayed her as too sus and made her the most obvious it actually just made her the least obvious candidate to be Rum. While she may be involved with another incident (probably Haneda Kouji's murder), there was no doubt in my mind that she wasnt Rum.
Kuroda (the big guy) is aware that Conan is the brains behind sleeping Kogoro, if he was Rum, there would have definitely been reprecussions to Shinichi's case.
Haibara has also noted that she doesnt feel the black organization aura coming off him.
He also has knowledge into Wakasa Rumi's past, since two of the suspects are connected to each other to me it made them less suspicious of being Rum.
Then theres sushi guy.
The sushi guy who forced himself to be involved with Kogoro's cases and almost always shows up unprompted but made it natural.
"Oh i just happened to be in the neighborhood to give you free sushi!"
Yeah no.
Honestly, it was a small thing but it really stood out in my eyes, thats why I believed sushi guy was Rum.
@Akera93
"Why the snipe"
Is referring to the translators, not what happened in the chapter lol