RIO DE JANEIRO —
The motive remained unknown, and investigators said it might never be discovered.
Oliveira was one of six children, a man who identified himself as one of the siblings told the Globo television network. The brother said Oliveira was adopted as a baby and had long suffered psychological problems, but he did not elaborate.
Oliveira was fascinated with guns, and was "very impressed" with the 9/11 attacks in the U.S., the brother added.
"He said, for example, that he had 'a lot of desire to destroy an airplane, like that guy did in the United States,'" said the brother, whose face was disguised at his request because he feared reprisals.
Oliveira attended the Tasso school from 1999 until 2002. He was considered a good student who didn't get into trouble, but who was estranged from the world around him.
Vanessa Nascimento, a neighbor of Oliveira, said he was "always very calm and closed."
"He wasn't one to make friends. But no one ever suspected he was capable of doing what he did," she said.
Reacting to the attack, congressmen began calling for even greater control over the sale of guns and ammunition in Brazil.
"There are mental health issues related to this tragedy, but it is also clear that if the access to weapons and ammunition were not so easy, the result would have been different," Congressman Alessandro Molon said after visiting the Tasso school.
Brazil already has strict gun laws.
A 2003 law sharply limited who could legally purchase firearms and carry guns on the street. Anyone wanting to buy a gun must be at least 25, pass a psychological test, prove they need the weapon, have no criminal record, and provide proof that they attended courses on handling guns.
However, Brazil's porous and long borders allow for illegal arms to easily flow in. Many firearms are in the hands of powerful drug gangs that control sprawling slums in cities across the country. Antigun groups estimate there are 16 million guns in Brazil — half of them illegal.