A security camera captured the moment when a student from the Thomazia Montoro State School, in São Paulo, stabbed and killed his 71-year-old science teacher, Elisabeth Tenreiro.
The 13-year-old teenager enters the classroom with a skull mask and a knife and assaults the teacher.
He then begins to attack his classmates, failing to seriously injure any of them.
A few minutes later, three teachers enter the room and manage to disarm the student.
The authorities have highlighted the value of Cintia, the physical education teacher, for being the one who finally takes the weapon from the minor.
The attacker's colleagues mentioned in interviews with the media that he had already talked about carrying out an attack of this type, without his friends taking it seriously.
In recent years, Brazil has been the scene of similar attacks on schools.
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