injured, and 341 are arrested. April April 1 The Community Charge (poll tax) takes effect in England and Wales amid widespread protests Strangeways Prison riot: The longest prison riot in Britain's history begins at Strangeways Prison in Manchester, and continues for 3 weeks and 3 days, until April 25. The 1990 United States Census begins. There are 248,709,873 residents in the U.S. April 6 – Robert Mapplethorpe's "The Perfect Moment" show of nude and homoerotic photographs opens at the Cincinnati Contemporary Arts Center, in spite of accusations of indecency by Citizens for Community Values. April 7 Iran–Contra affair: John Poindexter is found guilty of 5 charges for his part in the scandal; the convictions are later reversed on appeal. Scandinavian Star, a Bahamas-registered ferry, catches fire en route from Norway to Denmark, leaving 158 dead. April 8 In Nepal, Birendra of Nepal lifts a ban on political parties following violent protests. In the Greek legislative election, the conservative New Democracy wins the most seats in the Hellenic Parliament; its leader, Konstantinos Mitsotakis, becomes Prime Minister of Greece on April 11. In the Socialist Federal Republic of Yugoslavia, the Socialist Republic of Slovenia holds Yugoslavia's first multiparty election since 1938. After the election, a center-right coalition led by Lojze Peterle forms Yugoslavia's first non-Communist government since 1945. April 9 – Comet Austin, the brightest comet visible from Earth since 1975, makes its closest approach to the sun. April 12 – Lothar de Maizière becomes prime minister of East Germany, heading a conservative coalition that favors German reunification. April 13 – Cold War: The Soviet Union apologizes for the Katyn massacre. April 14 – Junk bond financier Michael Milken pleaded guilty to fraud-related charges. He agreed to pay US$500 million in restitution and was sentenced on November 21 to 10 years in jail. April 20 – 17-year-old Christopher Kerze goes missing in Eagan, Minnesota. He remains missing . April 21 – Japanese Yoshio Tani, M.Sc. murders gold merchant Turkka Elovirta and businessman Juhani Komulainen in Siuntio, Finland, having convinced them to buy a nonexistent 500 kilogram stash of Nazi gold. April 22 Lebanon hostage crisis: Lebanese kidnappers release American educator Robert Polhill, who had been held hostage since January 1987. Earth Day 20 is celebrated by millions worldwide. April 24 Cold War: West Germany and East Germany agree to merge currency and economies on July 1. STS-31: The Hubble Space Telescope is