Mahi Goyal

Okay! This is a really amazing book with a fantastic, nail biting, tripping over your seat plot. But I just want someone for me to clarify the dry ice thing. Ellie stole Janelle's pass and somehow got Hayes' fingerprints on it. That I totally understand. But she got her pass back the day Hayes died, before Hayes died, in the morning. So is the dry ice already planted there? Because of course it needs time to evaporate. Or is it that Ellie created some copy or something of the pass? Or is it something entirely else and I am interpreting all wrong? Please someone clarify this to me! Also why would Ellie kill Hayes? I mean she will blackmail him or something but killing. Why? Please answer that too!