Still waiting for Ryuji's thought regarding this episode .
Alright, I will try to explain it as briefly as possible.
First of all, like Yashiro said, it gave him the 'thrill' or 'filling something that's missing in this heart', when he kills someone.
Alright, the reason I put italic on the word 'kill', is because that it's not the feeling when he killed a certain person that it gave him thrills.
But rather it's when he 'killed them in style' and having a person framed. So killing him when he was in coma wouldn't give the 'thrill' that he desired for. In short, he is not your everyday psycho.
And it was never implied that he is planning to throw Satoru off the roof, are you perhaps talking about the opening? That's a different matter you know.
My thoughts on this episode,