Goma: At first glance there is nothing disturbing about the man playing tennis on the red clay courts of the Hotel Karibu. Other guests in the grounds of the hotel walk serenely across its manicured lawns, dine in thatched-roofed rondavels, or sip drinks while admiring Lake Kivu. The UN mission in Congo is the world's largest peacekeeping operation, costing $1.35bn a year. But instead of putting an end to an epidemic of rape and murder, the force is accused of actively supporting those it was meant to bring to justice.