As you say he left Canada at 9 but you skip the next 6 years...he trained with Al Qaeda, lived with Osama Bin Laden and was fighting at the age of 15 when he killed Sgt. Sheer and was captured by the US. He did have the choice as to kill or not during battle and he chose to kill Sgt. Sheer. Simply because he wants to recant his confession does not mean he did not do it there was evidence and testimony saying he did.
As for legal reason the widow has a judgement which can be enforced in Canada by an application to the Court. Commonly, in civil actions, when there is an understanding of a pending or potential application to enforce a judgement a debtor will pay the funds into court allowing parties to make submissions leaving a judge to determine who has the rights to the money this is what the government should have done given they decided to award a financial settlement. Check Wikipedia and you will see how the entire family has taken advantage of Canada.