RIO DE JANEIRO — A gunman roamed the halls of an elementary school in Rio de Janeiro on Thursday and killed 11 children, lining them up against a wall and shooting them in the head at point-blank range as he shouted, “I’m going to kill you all!”

It was the worst school shooting in Brazil — and would have been deadlier if the gunman had not been shot in the legs by a police officer, who said the man then fell down some stairs and shot himself in the head.

Images taken with a cell- phone and posted on YouTube showed students fleeing wildly, screaming for help, many with their white and blue school shirts soaked in blood.

At least 13 people, mostly students, were injured, many by gunfire, and taken to local hospitals, said Rio state Health Secretary Sergio Cortes. At least four were in grave condition.

The dead included 10 girls and one boy, plus the gunman, Cortes said.

“He came in shooting,” said Andreia Machado, recounting what her 13-year-old daughter, Thayane, told her before going into surgery.

Thayane was hit by three bullets and lost feeling in her legs because one hit her spine, said her mother. Crying as she spoke, Machado wondered if her daughter would ever be able to return to school — or walk.

“She’s such an active child,” she said. “That’s the biggest fear I have, her not being able to walk again. But we have to trust in God.”

The gunman was identified as Wellington Oliveira, 23, who had once attended the Tasso da Silveira school in a working-class neighborhood in western Rio.

No motive was known, but authorities said the shooter left a rambling and mostly incoherent letter at the scene indicating he wanted to kill himself.

The letter also explained in detail how Oliveira wanted his corpse to be cared for — bathed and wrapped in a white sheet that he left in a bag in the first room where he said he would start shooting. The letter also states that the gunman should not be touched by anyone who is “impure” unless they wear gloves.

“If possible I want to be buried next to my mother. A follower of God must visit my grave at least once. He must pray before my grave and ask God to forgive me for what I have done,” read the letter, portions of which were posted on the Globo television network’s website.

Edmar Peixoto, the deputy mayor of western Rio, said the letter also stated the gunman was infected with the AIDS virus.