Spanish investigators announced the arrest of another suspect in last month’s deadly train bombings, as a shadowy Islamic extremist group claiming links to al Qaeda threatened more attacks unless Spain immediately withdrew its troops from Iraq and Afghanistan. Forensics experts meanwhile tried to determine the precise number of suspects who blew themselves up in a suburban Madrid apartment during a police siege on Saturday. Police had said that five people were inside the apartment, but investigators on Monday said the scattered remains suggested that a sixth person may have been inside. Among those killed in the explosion in Leganes, a suburb 10 miles south of Madrid, was the man investigators said they considered the “brains” of the operation, Sarhane Ben Abdelmajid Fakhet, 35, known as “the Tunisian,” and the suspected operational commander, Jamal Ahmidan, known as “the Chinese.” Both were named in an international arrest warrant issued after the March 11 bombings of four rush-hour commuter trains in Madrid, in which 191 people were killed and more than 1,800 were wounded. Full Story