A gunman attacked a school Tuesday morning in Kazan, sending students running out of the building as smoke poured from its windows. At least 9 people were killed – 7 eighth-grade students, a teacher and another school worker - and 21 others were hospitalized.

Footage released by Russian media outlets showed students dressed in black and white running out of the building. Another video depicted shattered windows, billowing smoke and sounds resembling gunshots in the background. Dozens of ambulances lined up at the school’s entrance after the attack and police fenced off access to the building.

Officials said the attacker has been arrested and police opened a criminal investigation into the shooting. Authorities immediately put additional security measures into place in all schools in Kazan. Authorities announced a day of mourning on Wednesday to honor the victims of the shooting.

Russian media said the shooter was a former student of the school who reportedly called himself “a god” on his account on the messaging app Telegram and promised to “kill a large amount of biomass” on the morning of the shooting.