ZAGREB:The United Nations revealed on Tuesday that thieves broke into a UN office over the weekend and made off with computers that contained key documents on the investigation of war crimes in Croatia. "Most of our research concerning human rights violations, evictions and harrassments in Croatia is gone," said a UN spokesman. "It is a very heavy blow to our work." Most of the data, which had not been copied onto computer discs, concerned evidence gathered against Croats druing their offensive against Serbs last summer. At least a hundred civilians were killed and thousands of homes were looted and burned during the offensive, which is believed to have contributed to the Serb willingness to come to the negotiating table.