Two children were killed and 17 people, 14 of them children, were wounded Wednesday morning when a 23-year-old gunman opened fire on a mass at Annunication Church in Minneapolis.

All 17 of the wounded were expected to survive, the Star Tribune reported.

Three children remain hospitalized at Children’s Minnesota, the hospital said. Four others have been released. The remaining 10 wounded were at Hennepin County Medical Center, where six children and one adult were in critical condition.

The children were students at Annunciation Catholic School, which began its fall term on Monday. The students and others were assembled at the church Wednesday morning for their first mass of the school year, CrimeOnline previously reported.

The two students who were killed were 8 and 10, officials said. The other minor victims ranged in age from 6 to 15.

The gunman killed himself after the attack, which began as students were gathered for the morning mass.

“During the mass, a gunman approached on the outside on the side of the building and began firing a rifle through the church windows towards the children sitting in the pews at the mass. Shooting through the windows, he struck children and worshipers that were inside the building,” Minneapolis Police Chief Brian O’Hara said, according to the Star Tribune.

O’Hara said the gunman, identified as Robin Westman, was armed with a rifle, a shotgun, and a pistol, and used all three in the attack.

Investigators have not speculated a motive but said there was a video manifesto posted to YouTube, which has since been taken down. Investigators are looking through the videos posted there to determined why Westman decided to attack students at a school he had attended himself for a year.

According to The Associated Press, Westman displays weapons and ammunition in the videos. In one, he sings the word “tomorrow” and says, “I’m sorry to my family … that’s the only people I’m sorry to.”

In another video, he displays what appears to be a drawing of the layout of the church, points to two outside windows, and then stabs the drawing with a knife.

Additionally, sources said his mother had previously worked at the school, which serves pre-K through 8th grade students.