[Hojczyk]

Two problems…

Who left the door open….teacher or a kid or someone else

And I think the classroom door was fortified to keep people from getting in…

The question I have why not break the windows to get in..

[Lazamataz]

Two problems… Who left the door open….teacher or a kid or someone else

It's well-established that the teacher did.

The question I have why not break the windows to get in..

Excellent question. Almost all police have an entry tool meant to facilitate entry into hard-to-get-into places. I guaran-damned-tee you that, armed with one of those tools, I could get in through a window in less than 5 minutes.

[Bikkuri]

"The question I have why not break the windows to get in.."

It depends.. If there are children still alive in there (or if it was unknown whether there were still kids alive), it would be a huge risk to their (children's) lives.

On the other hand, if all kids where already murdered (and it is known they are all dead), then there is no reason not to do it that way (nor no reason not to blow the door inward).