A memorial of flowers and crosses has been created a Catholic church in Minneapolis, where a shooter fired through the windows the day before, killing two children and wounding 17 people.

Investigators are examining the videos, writings and movements of the shooter. They’re looking for connections to the church and its school to understand the motivation for the attack. Police Chief Brian O’Hara says Robin Westman fired dozens of rounds toward Annunciation Catholic School students sitting in the pews during Mass on Wednesday morning.

He says the shooter then died by suicide. Hours later, hundreds crowded inside a nearby school’s gym, clutching one another and wiping away tears during a vigil. Archbishop Bernard Hebda told a crowd of mourners Wednesday night that students tried to shield their classmates as the gunfire erupted.

AP video shot by Mark Vancleave