Saruwatari becoming more suspicious.Suddenly the other suspect killed herself just when the police starting suspecting…
Most likely she's the accomplice/executor, while the brain is one of the first 10 cast member. It's still waaay to early to speculate, but pretty much implied in episode 2 that somebody did pull some strings. My early guess is Doctor or Ogoma's senpai, the final 2 cast member announced are also suspicious.
4 more eps, this gonna ends with Cliffhanger isn't it.
Rather than we have a conclusion but a new threat appear in the ending (just like SPEC). It seems that we won't get any conclusion and straight up movie.
Celebrity 
It's still waaay to early to speculate, but pretty much implied in episode 2 that somebody did pull some strings. My early guess is Doctor or Ogoma's senpai, the final 2 cast member announced are also suspicious.
Shame because this is the duo who direct Keiji Yugami.
He appeared on red carpet, probably gonna be the "wild card" character or he's the protagonist of the flashback arc (if there's any).