Suppose Yashiro is the murderer, and his actions today served as hints. It can't be a coincidence that Yashiro appeared today. I say either he's tailing that Aya girl then suddenly spotted them and called it a day, or he was tailing Satoru so he can get a jump on him.
Last panel also got me thinking. You know Final Destination? You avoided Death but Death targeted a different one. What if the same applies here? What if that girl at the end was being targeted by the kidnapper too as a substitute for Hinadzuki?