CNN) -- Thursday's massacre of 11 students at a Brazilian school could have been even worse, were it not for the heroic actions of a military policeman, according to a statement from the Rio de Janeiro state governor's office.

Third Sgt. Marcio Alexandre Alves, 38, and a colleague raced to the Municipal School Tasso da Silveira in Realengo after they were approached by a student two blocks away from the school, who asked them for help, the governor's office said.

Upon arriving at the school, Alves heard gunshots and quickly climbed to the second floor. There, he confronted the heavily armed gunman coming out of a classroom, keeping the suspect from ascending to the third floor, where there were more students, the statement said.

Alves said he shot the gunman in the abdomen. When the suspect fell, he committed suicide by shooting himself in the head, according to the statement.

At that point, Alves looked for a second suspect he had heard was in the building, but that information turned out to be unfounded, the governor's office said.

Alves, an 18-year veteran of police work, said seeing the slain children gave him a great feeling of sadness.

"Scenes that will not be easily erased from my memory. I have a son that age," Alves said. "But it was also a sense of accomplishment. I wish I would've arrived there sooner (to save more children). Had I gotten there five minutes earlier, I could have avoided some deaths," the statement said.

Brazil's president has announced three days of national mourning.

Beyond the 11 students killed, another 13 were injured, four of whom were in critical condition, Rio Health Secretary Sergio Cortes said.

It is a very unfortunately ocassion that 11 people die and 13 were injured but there still person that have consciousness about that like the police man that shoot the shooteer in the building I think that he deserve an honor because many people wouldnt do nothing because they dont care I hope that situations like this stop happening because it happen in all the world.