Police crime scene investigators inspect the alley in which a Halloween stampede took place in the neighbourhood of Itaewon in Seoul. Photograph: Anthony Wallace/Getty Images South Korea’s president Yoon Suk-yeol declared a period of national mourning on Sunday after a Halloween crush killed some 151 people in a packed nightlife area in Seoul. Yoon expressed condolences to the victims, mostly teenagers and people in their 20s, and his wishes for a speedy recovery to the many injured. “This is truly tragic,” he said in a statement. “A tragedy and disaster, that should not have happened, took place in the heart…