If I was going to use a phone for remote listening/recording under circumstances like that, I'd actually take two phones with me. That would have been perfectly viable for Satoru with his number of allies. It's all well if Yashiro hadn't paid any attention to begin with, but as it was, he totally ceased to pay any attention whatsoever once he got the first (obvious) phone from Satoru. I can't even blame Yashiro because after 15 years of waiting, he probably wasn't in a perfectly calm and cool state either.

But yeah, this is Japan. Once you get accused, it must be 90% sure you'll get declared guilty. Since Yashiro was taken away by the police in that manner, he was finished. He would lose his allies immediately as they wouldn't care to wait for the verdict in that land where face and reputation is everything. Without those allies, his situation is hopeless in the system. After all, he had some profile, so taking credit for his arrest, accusation, and judging will boost other people's careers.