It was Shuichi who left the coaster as Subaru for Jodie

Chapter- 699-704

Everything what happened there and why Shuichi was the one who left the coater makes sense logically. Let's have a look step by step, how it actually worked-

A Mind Game

How Jodie would have percived and reacted towards the message-

As soon as Jodie got the message, she thought about Shuichi. In the message, a particular word which only Shuichi uses in the whole DC universe was used-"area". So logically she would have thought and would have followed about Scar Akai.

Imo Gosho uses english words and phrases to show that he is a foreigner and to depict his identity through which we can know it's him. Ex- 50-50 was used in scarlet return, so that Jodie will know that Subaru is Shuichi and so on. After this chapter, in bell tree express, Subaru uses the same word infront of Haibara.

Another small observation was the coaster was folded at the left side. This implied that the person who folded the coaster was lefty. He wrote the message and, flipped it and put it under the glass. You know Gosho ia detail oriented afterall ;)

Now Subaru left the message while Jodie was away from her table because she was answering James. Co-incidence? No. Imo it was Shuichi who informed James and asked him to call her back.

Now why Shuichi left the message when James already asked her to come back? Don't think that she would have left that easily. It wasn't only for personal reasons but also for professional reasons which is absolutely valid. Professionally, to figure out another a deceased colleague is already a good reason to stay back there. So Shuichi left a warning message to her so that she'll leave as soon as possible.

The plan would have backfired ONLY when Jodie would have INTERACTED with scar Akai. But Shuichi made sure that shouldn't happen. He did that at the same time while saving Jodie's life. And she lost him!

How scar Akai would have reacted to Jodie?

When Jodie was calling him out, Scar Akai would have thought that she is only spotted her colleague who seemed to have personal connections with him. So when she shouted, that wouldn't have intervened in his deduction.

Bourbon ( Scar Akai) would have tried his best not to get caught by any FBI agents, especially the ones he was already spotted by, or else they would have taken him with them. All he needed was reaction, nothing more. Jodie was already suspicious that how come no one remember a man having scar in the mall. So we are talking about Bourbon, he won't commit this silly mistake.

When Scar Akai went outside of the mall, he looked directly towards Chianti. That means he knew before that they thought his as Akai Shuichi and we're there kill him. So Jodie's reaction was logical according to the situation.

Speculation- I don't think he would have checked on a particular person for twice. Even if we think logically Gosho won't do that twice when in the Detective boys vs bank robbers, Jodie gave the reaction which was enough to know the truth. Imo, Bourbon would have observed while investigation that Jodie usually is seen with Camel and James so he targeted them as well.

The situation was played smoothly by Shuichi. Basically he took advantage of the situation to save his colleagues by manipulating everyone, got information about Scar Akai and his identity was secured. Hats off to that guy! Basically hats off to Gosho!