[Renall]

I think you're complicating things overmuch.

Spoiler for The 'Test':

Nobody had to order a "test." That could just be an excuse to lure the children and Gohda/Kumasawa (assuming that none of them are in on it, anyway) out one by one. It's a little odd that the hostage-taker isn't interested in speaking to them, isn't it? After all, you don't want people to send each other coded messages with expressions that you don't know about. Of course, if one or more of the people making phone calls was actually a responsible culprit, you could say the hostage-taker was speaking directly.