A gunmen opened fire in an elementary school in Brazil killing at least 12 students Thursday in what crime experts are calling the worst school massacre in Brazil's history.

The dead included 10 girls and two boys. At least three students wounded in the attack were in critical condition.

Cell phone video captured at the scene showed panicked students fleeing the school.

Police identified the shooter as Wellington Oliveira, 23, a former student at the school.

Witnesses said he entered the Tasso da Silveira school in Rio de Janeiro on Thursday armed with two pistols and an ammunition belt, shooting at students and repeatedly yelling: "I'm going to kill you all!"

"He had already killed a lot of children in the first floor and in the yard," student Jade Ramos told the Globo Television Network. "He kept telling the kids to face the wall and was shooting at their heads. The children kept begging, 'No, please!' There was a lot of blood, children agonizing on the stairs."

CBN News spoke with Erni Seibert of the Brazil Bible Society, who said local pastors rushed to the scene to help victims.

Oliveira took his own life after police gunfire struck his legs and sent him toppling down some stairs.

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 Arabic news service al-Arabiya has reported that Oliveira was a convert to Islam.

Rio Gov. Sergio Cabral called the shooter a "psychopath" and said there were no indications anyone else was involved in the shooting, but that the investigation would continue.

"We have to investigate where he got the weapons and where he learned to use them," the governor said.