Heckler & Koch, Germany's biggest manufacturer of small arms, may have supplied some of the weapons used in the September killing of several students in Iguala, Mexico...Mexican investigators seized 36 rifles made by the German firm from local police...Six student-teachers were killed in Iguala in the state of Guerrero on September 26 when police fired at buses carrying more than a hundred people on their way to a demonstration. Later, a number of students were allegedly rounded up by police and handed over to the criminal gang Guerreros Unidos. Of those, 43 are still missing...The German government approved the sale of around 9,500 G36 rifles to Mexico in 2007, on condition that they would not be used in four states, including Guerrero, where security forces were considered particularly corrupt. In 2010, media reports showed the rifles were being used by security forces there, and alleged that H&K employees had helped trained officers to use them...