Saari entered through the school buildings via the basement.
The shooting began in a classroom at around 10:40 (UTC+3), when roughly 200 people were assembled inside the college.
The emergency services received their first call at 10:46, after Saari stopped shooting in the classroom.
Saari was armed with a .22 LR caliber Walther P22 Target semi-automatic firearm and homemade Molotov cocktails.
He wore dark clothing and a balaclava (ski mask).
The school's caretaker Jukka Forsberg, who had several shots directed at him but survived, said "[The gunman] was very well prepared.
He walked calmly."

Saari initially opened fire on a group of students taking a business studies exam, and entered at least one other classroom.
According to the three students who were able to escape from the exam room (there were roughly 20 students taking the exam), Saari had approached his victims individually before shooting them.
It was also said that he was revelling in the situation and was acting very aggressively.
Saari encountered little resistance, and the massacre was concluded relatively quickly.
He left the exam room at least once during the massacre to reload in the hallway and, according to witnesses, the teacher unsuccessfully attempted to prevent him from returning and was killed.
Nine victims died in the exam room and the tenth victim died in the hallway outside the exam room.
Another student was seriously wounded in the head but survived.
Saari then covered the classroom in a flammable liquid, believed to be petrol, and set the room alight.
Some of the victims' bodies were damaged by the fire started by Saari, making it more difficult to identify them.

A student in an adjacent classroom, Sanna Orpana, said that her class had heard "shooting and a kind of a rumble like tables falling down."
Orpana believed at the time that the noise may have been coming from a toy gun, and two other students went to investigate the noise.
Saari shot at them, and the remaining students in Orpana's classroom hid under a table before running upstairs.
At some point between 10:45–11:00 Saari ran down a corridor and threw a Molotov cocktail into a language laboratory.
He then shot out all of the windows in the school's main corridor, that extended through the building.
It was during this time that he also took aim at Forsberg.

A police van with two officers arrived a short time after the shootings began, at around 11:00.
They entered the yard of the college where they were shot at by Saari, and forced to retreat.
From around 11:45 to 12:00 further police units, bolstered by a number of armoured vehicles, began to arrive on the scene.
They attempted to enter the building through the main corridor, but this assault was aborted due to the black smoke that was emanating from within the building.
Saari entered through the school buildings via the basement. The shooting began in a classroom at around 10:40 (UTC+3), when roughly 200 people were assembled inside the college. The emergency services received their first call at 10:46, after Saari stopped shooting in the classroom. Saari was armed with a .22 LR caliber Walther P22 Target semi-automatic firearm and homemade Molotov cocktails. He wore dark clothing and a balaclava (ski mask). The school's caretaker Jukka Forsberg, who had several shots directed at him but survived, said "[The gunman] was very well prepared. He walked calmly."
Saari initially opened fire on a group of students taking a business studies exam, and entered at least one other classroom. According to the three students who were able to escape from the exam room (there were roughly 20 students taking the exam), Saari had approached his victims individually before shooting them. It was also said that he was revelling in the situation and was acting very aggressively. Saari encountered little resistance, and the massacre was concluded relatively quickly. He left the exam room at least once during the massacre to reload in the hallway and, according to witnesses, the teacher unsuccessfully attempted to prevent him from returning and was killed. Nine victims died in the exam room and the tenth victim died in the hallway outside the exam room. Another student was seriously wounded in the head but survived. Saari then covered the classroom in a flammable liquid, believed to be petrol, and set the room alight. Some of the victims' bodies were damaged by the fire started by Saari, making it more difficult to identify them.
A student in an adjacent classroom, Sanna Orpana, said that her class had heard "shooting and a kind of a rumble like tables falling down." Orpana believed at the time that the noise may have been coming from a toy gun, and two other students went to investigate the noise. Saari shot at them, and the remaining students in Orpana's classroom hid under a table before running upstairs. At some point between 10:45–11:00 Saari ran down a corridor and threw a Molotov cocktail into a language laboratory. He then shot out all of the windows in the school's main corridor, that extended through the building. It was during this time that he also took aim at Forsberg.
A police van with two officers arrived a short time after the shootings began, at around 11:00. They entered the yard of the college where they were shot at by Saari, and forced to retreat. From around 11:45 to 12:00 further police units, bolstered by a number of armoured vehicles, began to arrive on the scene. They attempted to enter the building through the main corridor, but this assault was aborted due to the black smoke that was emanating from within the building.
Kauhajoki school shooting