An extremist Swedish group claimed responsibility Monday for 9 arson and bombing attacks, and threatened to unleash a killing spree at the 2004 Olympics if the Games are awarded to Stockholm. Last week, the same Swedish group claimed it planted the August 8 bomb that wrecked a portion of Stockholm’s old Olympic stadium, where the 1912 Olympic Games were held. Swedish police said that note probably was not written by those responsible for the blast. Stockholm is 1 of 5 candidates for the 2004 Olympics, which will be awarded on September 5. The others are Rome, Athens, Buenos Aires, and Cape Town.