To save taxpayer money on legal fees (the trial must be completed and a decision rendered before the court can award compensation) and have some control in the amount you pay out instead of risking the court giving more than the 20 million Khadr's lawyer was asking for (again saving taxpayer money). Governments before Harper behaved in this manner when facing a certain loss in court. It's the rssponsible, and probably unpopular, thing to do.