The teen was arrested after the rampage at a school in Ostroleka, 120 kilometers from Warsaw, said police, who released a blurred photo following his arrest. Mariusz Frankowski, the top local official, said five students, two teachers and two passersby were injured, AFP reported.

“The lives of none of the injured are in danger,” Mariusz Zeranski, Ostroleka police spokesman, told reporters.

Elzbieta Lukasiewicz from the Ostroleka prosecutor’s office said, “The boy entered the school and attacked the students and teachers with a dangerous tool.”

The teen was arrested by the police about 20 minutes after the attack, not far away from the school. He was treated by emergency services after having “self-harmed,” the prosecutor’s office said. He is now out of hospital and in police custody.

Bomb disposal experts took away a bag the assailant had left at the high school. The school was closed as a precautionary measure.

The attack comes just a few days after a priest was stabbed by a Ukrainian in a monastery in a Polish region near Ukraine. Social networks on Wednesday were again full of rumors that the attacker was Ukrainian.