In Uri, Why Vicky's character didn't kill the terrorist kid?

Why Vicky's character Vihaan in Uri, didn't kill the Pakistani terrorist kid? Instead he just locked him in a room. What was that for? The kid is holding a rifle, and living with terrorists. He was no innocent. He was a terrorist as well. There was no need to show pity on him. Sparing his life will do no good. He will grow up and become just like them, whom the Indian army was killing .