The theme of this arc seems to be mistaken identities. It makes sense after the B.O. chapter. Here is the recap of the points everyone has brought up so far.
Kobayashi didn't hear the voice from among the suspects although she didn't listen to the man's voice. Kobayashi noted that the voice was a deeper woman's voice. That makes is likely that voice she heard was the victim's given her build. That means the victim, Sumida, was ordering someone, probably the murderer to, "Listen up, hand it over!! I'll kill you!!".
Kagitani Kikuna hated Sumida because she kept her mother's ring when Kagitani failed to make payments for it in a timely fashion. Sumida could have been yelling at her to return the ring if Kagitani had forcefully retaken it. I didn't see the ring on the victim's hands, but given the positioning it is hard to tell if there is a ring or not. Also it isn't clear if Sumida would have been wearing it at the time of the crime.
Takimoto Ryouko had a grudge against Sumida because she conned her with a replica plate. Ryouko does not seem to have anything that Sumida would want at that moment, unless Ryouko was blackmailing her somehow...
Kodama Ryuusuke had borrowed 5,000,000 yen from the victim. It makes perfect sense for the victim to tell him to hand it over. If he was carrying something thin and rectangular with his right arm which is possible given the pictures, he would appear to have breasts when seen in profile. He also has long hair that could be tied back in a ponytail. It would not be strange for him to be out on the street because of his job. (See
host club to see what I mean) Finally, although it isn't clear if it is relevant yet, Kodama had a left shoulder injury. If he was a pitcher, that would make him left handed. When I carry things under one arm, I usually use my dominant hand side, which means that if left handed, Ryuusuke would be using his off hand. It is also possible that Ryuusuke was not a pitcher and injured his off arm somehow.
As for the letters on the van, they are probably not numbers but letters. The possibilities are either "OS" or "DS".
Possibilities include "H
OST CLUB" (I don't think one of those would have a van though...) or the more likely "
OSAKA Nico-Nico Transportation" which Mitsuhiko confirmed had its name written on the side of it and had gotten lost in the vicinity which puts it at the right time and place for the crime. Hopefully the van people get questioned because Conan had some suspicious sweatdrops in the first chapter when the topic of the professor helping someone move came up.
We might have one more chapter of case before the dénouement since we are currently lacking definitive evidence. In the meanwhile, my money is on Kodama Ryuusuke since he has the best motive and he fits with the theme of mistaken identities. I wonder if he will try to invite Kobayashi out to his host club to finish her off after he overheard Shiratori's failed confession...
Prediction one: The culprit tries to attack Kobayashi who is saved by Shiratori.
Prediction two: Kobayashi being saved by Shiratori triggers a flashback to the events of the bookstore. I don't know if that will be enough to alleviate Kobayashi's grumpiness.
Prediction three: The culprit tries to attack Sato thinking she is Kobayashi and then gets served a whopping dose of pain Miwako style.
Prediction four: Sato and Kobayashi finally meet face to face.