What really happened?

The overall story was really indeed and amazing one, but the last episode still left some question on my mind like did the boy really push his sister or maybe he could have saved her but didn't because when the boy was giving his statements to the police he's face showed her didn't tell the truth or maybe am wrong about this, it's just merely my own little question and assumptions going on in my head right now.

funny female lead

currently watching this drama,and i can say so far so good.The female lead is so funny and her acting skill is amazing...so loving this drama