I´m not as positive about Yuuki as you guys. I agree that he´s left out of the big picture at the moment and he has to come in at some point for the finale. Him being the savior might be an option.

Him being ANOTHER killer might be also an option. Yashiro planned to kill Kayo, that much is right. He then likely switched to that bully-girl that was by herself now. And when he realized it was Satoru, who got in his way, he took that boy "to fill the hole in his heart".

That doesn´t mean the other girls would have been murdered by Yashiro, too. We KNOW that Yuuki is also close to that girl that now visits their hideout. And since the teacher was no red herring, and we all assumed that he´d be too obvious of a choice, MAYBE the fact is, there are no red herrings. Now that would make for a shocking twist, I think. I picture it like this: Either Kenya saves Satoru or Yashiro saves him himself because of the "I saw your future" line. They go back, either gettin Yashiro to the police OR letting him go because of some serious talk, where they are convinced that Yashiro will never again attempt a crime. THEN, *gasp*, they find out that the girl from their hideout has been kidnapped/murdered. And something quickly hints at Yuuki, making it all the more tragic.

After all, there´s at least 2, maybe 3 more episodes, right? These will be either about chasing Yashiro or dealing with a twist.