Whoever killed the carp came back later to finish off the remaining ornamental goldfish and gut them with the skill of a chef. At the nearby WHO headquarters, meanwhile, elevators have been defaced with grafitti. 'Death to Nakajima,' one says.
Rarely in the fractious history of the United Nations has the leader of one of its agencies been as unpopular as Dr Nakajima. During his tempestuous reign he seems to have alienated most of his staff and leading donors, including the European Community and the United States.
To their intense dismay, Dr Nakajima is seeking re-election this month for a further five-year term, when the WHO's board of governors, made up of member states, will cast their secret ballots for a new director-general.
Dr Nakajima is heavily backed by the Japanese government, which gave dollars 51m to the WHO last year and is trying to fashion a role for itself on the world stage.
According to a leaked briefing paper from the State Department in Washington, Japanese actions, 'some reported and others verified, amount to a pattern of aggressive tactics, including pursuit of votes in exchange for favours'.
Among the complaints of vote- buying is an allegation by the government of the Maldives - which is on WHO's board - that Japan threatened to stop importing fish should Dr Nakajima be defeated in the secret ballot. The US alleges that Jamaica was threatened with the loss of coffee exports and that Algeria was warned that a dollars 250m loan by the Export-Import Bank would not go through. Among other charges is an allegation that a Japanese diplomat offered a job to an official of the US Agency for International Development if he agreed to lobby on Dr Nakajima's behalf.
The Europeans and their friends are backing Mohammed Abdelmoumene, the deputy director who was fired from his job after announcing his candidacy late last year.
US officials have sent out veiled warnings that the WHO, with a budget of dollars 900m,will be put in the international doghouse if Tokyo's campaign is successful.
Opposition to the Japanese director-general has been growing since 1990, when the Independent on Sunday first reported a collapse in staff morale and a slowdown in the WHO's important work. Dr Nakajima's managerial style was widely blamed.
Disgruntled staff complain that Dr Nakajima, 63 and married to an American, is difficult and sometimes impossible to understand in either French or English. Diplomats say he lacks the communications skills necessary for such a complex job, and that he spends too much time travelling around the world.
His defenders say he is a competent administrator and that he is only doing his job when he visits the WHO's highly decentralised regional offices.
Dr Nakajima, the 10th in a long line of doctors in his family, is an avid art collector, and after an official trip to the Soviet Union in 1981, he walked into a barrage of public criticism when it was alleged that he was detained by customs officials who asked why he was taking six valuable icons out of the country.
In the ensuing flap, Dr Nakajima blamed his Russian guide for not telling him that he had to fill out customs documents before checking his suitcase through Moscow airport. The suitcase showed up in Geneva 24 hours later, without the icons.
Russian newspaper stories about the incident soon began circulating, but it was only when the Western press published details last summer that the WHO responded. It issued a statement saying that Russian customs officials had said that Dr Nakajima had not infringed regulations and that he had not been detained at the airport.