what do you think the boy in Twelve angry men felt and thought about when he was accused of killing his father?

To start, we don't know whether the boy actually committed the crime. If he hadn't committed the murder, he would have had feelings of terror and injustice. He would also have been in the midst of grieving for the man he did not kill.

If he had committed the murder, he'd still have feelings of terror and perhaps guilt. He also might be attempting to figure what type of clues he'd left behind.