The guy was brainwashed as a child by his lunatic father and dragged to Afghanistan to resist American's invasion. There was some kind of firefight, he nearly died, and the Americans decided that since he survived he was guilty of all the crimes.
He was 15. A kid. A child soldier, by international law.
He was held for a decade in Guantanamo Bay, a US military facility, without any real trial.
The US already had him. They abused his rights and ignored international law. Why should Canada give him back to them?
Of course, the difference here was that the USA attempted a diplomatic process and did not execute a citizen on Canadian soil.
You seem to be implying that if India couldn't extradite him, they should kill him.