"He has been an employee since 2008 and has never had a bad record so we could never have anticipated something of this nature happening", Mayor of Janauba, Carlos Isaildon Mendes, told the media.
Although a police investigation has begun it is not yet known what led the security guard named locally as Damiao Soares dos Santos, aged 50, to carryout the attack which left 15 others in serious condition in hospital.
Four children and their teacher were killed Thursday at their preschool in Brazil when a security guard set them alight.
About 50 people were sent to hospital with injuries, said Bruno Ataide Santos, director of the local hospital.
The attacker threw gasoline on himself, the children and the nursery before setting the whole room on fire.More news: Welwyn Hatfield MP Grant Shapps calls for leadership contest
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"My little girl was so good, so smart", he said of his dead daughter Ana Clara Ferreira.
Police said officers went to the suspect's home and visited his relatives to try to understand the motive for the attack.
"I was thinking of changing nursery schools because we are preparing to move".
But superintendent Renato Nunes told the website of the Hoje em Dia newspaper that the guard had "mental problems" since 2014. The children ranged in age from 1 to 4 years old.
"I deeply regret this tragedy with the children in Janaúba (MG). I want to express my solidarity with the families". I, who am a father, imagine that this must be a most painful loss.