Two children lost their lives, and 17 individuals, including 14 children, were injured on Wednesday morning when a 23-year-old gunman opened fire during a mass at Annunciation Church in Minneapolis.

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

Three of the severely injured children are currently receiving treatment at Children’s Minnesota, as reported by the hospital. Four other children have been discharged. The other 10 injured are being treated at Hennepin County Medical Center, where six children and one adult remain in critical condition.

The young victims were students at Annunciation Catholic School, which had kicked off its fall term on Monday. The children and others had gathered at the church on Wednesday morning to attend their first mass of the new school year, as 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 from the outside of the building and started firing a rifle through the church windows targeting children seated in the pews,” mentioned Minneapolis Police Chief Brian O’Hara, in a statement 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.

Authorities have not yet determined a motive, but disclosed there was a video manifesto uploaded to YouTube, which has now been removed. Investigators are reviewing these videos to understand why Westman chose to target students at the school he once attended.

According to The Associated Press, Westman showcases weapons and ammunition in his videos. In one particular video, he repeatedly sings the word “tomorrow” and states, “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.