BTTT Well said.
Check out the video half way down at this link labeled “(Watch a student’s recording of police responding to loud bangs )
http://www.cnn.com/2007/US/04/16/vtech.shooting/index.html
What the hell are they doing?
< What the hell are they doing? >
You can hear lots of shots in the background, which is either the perp killing the many students, or perhaps shots exchanged in a shootout with LEOs. It probably was the sound of the perp shooting the students, since we are hearing that the perp killed himself and was not shot by police.
I think the police officers we see in the video either were waiting for someone with a boltcutter to cut the chain off the door (and then we see them rushing the door), or they were securing a person on the sidewalk who they thought might be one of the shooters but was not, while at the time the actual shooter was doing the shooting inside the building.