RIO DE JANEIRO » Parents screamed in anguish and clung to coffins Friday as families buried most of the 12 children gunned down in the halls of their elementary school. A black police helicopter dropped white rose petals over mourners and a nation was left struggling for answers.

More than a thousand people gathered for the first funerals, held at a cemetery atop a hill overlooking the working-class neighborhood where the school shooting took place a day earlier.

"My love! My love!" screamed Noelia Rocha as the body of her 12-year-old daughter, Mariana, was placed in a white-walled cement tomb. As pallbearers placed a cover on top of the tomb, the mother wept uncontrollably before medical personnel on standby guided her away.

A man who family members said was the father of 15-year-old student Gessica Pereira helped carry her coffin, but he appeared disoriented and struggled to stay upright.

Upon placing Gessica’s casket in her tomb the man yelled out, "Go with God!" then began clapping. A large crowd joined him.

Funerals were held Friday for 11 of the 12 children killed in the shooting, following the Brazilian tradition of holding services within a day of a person’s death. Officials said a 13-year-old girl killed in the rampage will be cremated on Saturday.

Ten girls and two boys ranging in age from 12 to 15 were gunned down inside the Tasso da Silveira public school Thursday, most lined up along a wall and shot in the head at point-blank range.

The shooter, whom police identified as 23-year-old Wellington Oliveira, was carrying two revolvers, and shot and killed himself after being confronted by authorities. At least 12 other students were injured. Two are in grave condition.

A few details began to emerge about Oliveira: that he was a good student with a history of psychological problems who attended the Tasso school; that he showed a fascination with the 9/11 attacks in the U.S.; and that he spent a lot of time on his computer watching videos about how to fire weapons. Still, those who knew him said he did not seem the type to carry out such an act of violence.

Gessica Pereira’s uncle, Edmilson Santos, said at her funeral that the shootings were an incredible blow to the working-class Realengo neighborhood in western Rio. The school was located in the neighborhood and most victims — as well as the gunman — had lived there.

"We’re all part of a tight community. Everybody knew each other," Santos said. "I even knew the shooter. We met several times playing football."

Rio Mayor Eduardo Paes attended the first funerals.

"This is a tragedy that shook the city. Nothing we can do will bring the children back," he said. "All we can do now is offer comfort to the families, and that’s what we’re doing here."

At the school Friday, neighbors milled about in a daze and left flowers along a wall of the school already lined with 12 crosses. The name of each victim was written on a white piece of paper placed above each cross.

Officials posted the schedule of funerals on the school gate, and teachers left messages on a blackboard in the school yard imploring for better security in Brazil’s schools.

Guvete Antunes, who lives across the street from the school, sobbed as she tried to make sense of the massacre.

"What an absurd thing!" she said. "Children came running out of that school, desperate, with gunshot wounds, banging on my door and screaming, ‘Auntie, please help us!"’

The shock of the killings reverberated across the South American country.

"This is completely outside of our reality. This gunman lived in his own sick world and unfortunately brought his ugliness into ours," said Rivaldo Silva, eyes brimming with tears as he looked at newspaper headlines at a newsstand in central Sao Paulo. "I’m certain he was sent straight to hell."

The shootings turned the school, which was celebrating its 40th anniversary Thursday, into a nightmarish scene of bullet holes and blood marking the walls of classrooms.

Witnesses said the gunman stalked the halls, lining up children and shooting them one after the other in the head as they begged for him to stop.

The shooter took his own life after police gunfire struck his legs and sent him toppling down some stairs, but not before carrying out what crime experts said was the worst school massacre in Brazil’s history.

Witnesses said he entered the school armed with two pistols and an ammunition belt, shooting at students and repeatedly yelling: "I’m going to kill you all!"

The motive for the attack wasn’t 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.

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’s adoptive mother got him psychological treatment, but in recent years Oliveira refused help, the brother said.

Their adoptive mother died a year ago and their adoptive father died five years ago, the brother said.

Oliveria was fascinated with guns, the brother said, and was "very impressed" with the 9/11 attacks in the U.S.

"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.

"He was an adolescent who always kept to himself, apart from everything," the brother said. "He never established relationships with anyone. He never dated and had very few friends. He was a very introverted person and he was the same way at school."

Bruno Linhares de Almeida, who knew Oliveira for several years, told Globo, "He wasn’t very normal. Girls rejected 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."