isiolo kenya expel student shoot dead six former schoolmates security guard school northern kenya saturday lynch furious mob officials say attack take place school remote town lokichogio kenya turkana region close border war-torn south sudan least six students fly hospital bullet wound assailant 17-year-old south sudan one thousands refugee children live kenya go school since civil war break country 2013. detain possession ak-47 basic assault rifle choice conflict across africa middle east school attack bandits errant student expulsion disciplinary case regional government official wanyama musyambohe tell reporters security officials say assailant whose name disclose arrest kill mob police custody attack ... painful reminder state insecurity along border tweet turkana county governor josphat nanok close million people flee south sudan since fight break december 2013 spark become africa large cross-border exodus since 1994 rwandan genocide 75,000 kenya perennial conflict leave region awash arm smuggle across border relative ease expel refugee student kill seven kenyan school