RIO DE JANEIRO—At least 11 people, mostly children, died Thursday and more that 15 were wounded when an armed man attacked a school in Realengo in the poor suburbs of Rio de Janeiro. Police initially said that 13 people had died, but Rio de Janeiro’s Health Ministry later lowered the death toll. [...] Police Col. Djalma Beltrami said the killer used two handguns and a lot of ammunition. The suspect left behind a letter, in which he anticipated committing suicide after the attack. Beltrami, however, gave no details of any possible motive. Beltrami described the letter as “the words of...