There is absolutely no way they did not know kids and teachers were behind those doors. If they had to ask for a key then that means they spoke to school staff. The staff would have told them kids and teachers were in that room.
They made a purposeful decision to leave him in that class with those children. Gunshots could be heard in every video. They knew he was shooting them one by one and they LET IT HAPPEN.
The mayor is a bigot who speaks about immigrants all the time. He did so on Fox news last night. The kid wasnt even an immigrant. The police of the town harrass the residents and ask them for their papers all the time ( some reports from people who live there say)
Bias is a real thing and it is a factor in how police handle minorities.