The Afghans who took the Ariana 727 are still here because they are legally refugees: persons fleeing persecution or well-founded fear of persecution, as laid down in the UN Convention on Refugees. As I recall, it later came out that the hijack was a put-up job to get out of Afghanistan and everyone on the aircraft was more or less in agreement, still less did anybody get hurt. We can't send 'em back for nicking one of Mullah Omar's aeroplanes...
BTW: Good luck to the Ethiopian cops!