He killed a dozen schoolchildren and then himself. And while he was clearly mentally disturbed, his left over notes and videos paint the picture of someone who also felt intensely bullied as a child.
"I hope this serves as a lesson, especially to those school officials who stood by with their arms crossed as students were being attacked, humiliated, ridiculed and who were being disrespected," Wellington Oliveira videotaped himself saying only days before last week's massacre in Rio de Janeiro.
The 23-year-old pointed two illegally purchased revolvers for emphasis -- one at the camera, another at his head.
"Schools and universities are places for learning. This is where people are supposed to learn how to respect. If these officials had uncrossed their arms earlier and done something to fight against these types of practices, what happened may not have happened at all. I would still be alive. All those who I killed would still be alive," Oliveira said on the video, which was found on a computer near the school and made public Friday.
Oliveira's old classmates confirm he frequently suffered from bullying, which may be as prevalent in Brazil as any other country, but remains so unacknowledged in the culture that there is no precise Portuguese-language word for it.
"After this tragedy in Rio, Brazil is waking up to this problem of bullying," said Rivane Pedra, president of an anti-bullying center in Brasilia.
Emotional and physical violence between schoolchildren is common but unmonitored in Brazil, with virtually no federal efforts to educate teachers or students on preventing violence in schools, she said. "There has been essentially no support from the federal government on it. There are efforts to combat bullying, but it's from private groups or at the level of local governments."
Brazil had largely been spared mass shootings until now, which makes Olveira's act difficult to comprehend. Many here still think of school shootings -- and bullying -- as foreign concepts, something they might see in news from another country or in movies, not in a public school in one of Rio's working-class neighborhood.
"Brazil is a place of mixed races and I think we generally know how to get along with one another more," 18-year-old journalism student Tamy Cenamo said as she relaxed outside her school in central Sao Paulo. "This concept of 'bullying,' and the fact that we have no real word for it, tells you it was imported here."
But Pedra, who travels across Brazil to raise awareness on the issue, said there has been enough violence in the schools to warrant a nationally coordinated response. Teachers desperately need support and training on how to stop bullying, and students need programs to reinforce what is right and wrong, she said.
Oliveira committed suicide after being shot in the legs by police, and post-mortem psychological analysis is difficult, experts say.
Bullying alone can't explain why he shot 12 children, lining kids up along a wall and executing them at point-blank range.
As U.S. and European psychiatrists have learned while examining school shootings in their own countries, complex factors likely contributed to the attack -- mental illness that took a violent turn, childhood trauma and, yes, bullying that gave the shooter a way to justify the murders, said Dr. Talvane de Moraes, a forensic psychiatrist and professor at the Federal University of Rio de Janeiro.
The writings and videos Oliveira left behind are rambling and rife with religious overtones and quotations that don't adhere to any particular creed.
The known evidence -- that his birth mother suffered from schizophrenia, that his adopted family said he long suffered from mental issues, that he was anti-social from a young age -- point to him also being a schizophrenic, Moraes said.
Yet most schizophrenics are not violent. And so experts are looking to his past, his surroundings, and the bullying he repeatedly mentioned in the videos.
Former classmates confirmed that Oliveira was wickedly teased and physically abused by other students. They said he simply took the punishment, never fighting back or showing any violent tendencies.
He tried his best to simply become invisible, his family and classmates said.
The videos suggest that in his isolation, he was seething.
"Most people disrespect me. They think I'm an idiot, they take advantage of my goodness, they're prejudiced against me," Oliveira recorded himself saying in July 2010. "People will find out who I am in the most radical way in an action carried out for those like me, who are humiliated, beaten, abused in various places, mostly in schools and colleges, because they are different."
His tone and word choice are strikingly similar to that of Seung-Hui Cho, the Virginia Tech student who in 2007 shot 32 people to death and committed suicide. In Cho's videos, available online with Portuguese subtitles, he said he would die "to inspire generations of the weak and defenseless."
Oliveira also said he hoped to inspire others, and mimicked Cho's poses in two still photos that can be seen on the Internet: In one, he held a pistol in each hand with his arms outstretched; in another, he aimed the barrel directly at the camera.
In a letter police found at Wellington's house after the shootings, he cited the Virginia Tech gunman and another Brazilian shooter as icons in a brotherhood against bullies, and wrote that he, too, was "often assaulted by a group, and everybody nearby would mock me, reveled in the humiliation I suffered."
"Our fight is against cruel, cowardly people who take advantage of the kindness, the innocence, the weakness of people who are incapable of defending themselves," Oliveira said in one of his last videos.
But why kill 12 innocent children, ages 11 to 15, who were only infants when Oliveira attended their school?
"There is no simple connection between bullying and school shooters. In some cases, shooters have been picked on, but this fact does not distinguish them from millions of other youths who have been picked on. Thus, bullying by itself does not cause school shootings," Dr. Peter Langman, who studied 10 school shooters in his 2009 book, "Why Kids Kill: Inside the Minds of School Shooters," explained in an email.
"I think that people focus more on bullying than psychosis because it is easier for many people to comprehend," he added.
By Bradley Brooks of the Associated Press