All doors were locked automatically at 9:15.
At 9:30 the front glass was shot out. The school office is right there as you come in the front door so as the principal walked out of her office she would have been face to face with Lanza. At about that time 911 calls were made.
3-5 minutes after the first 911 call came in the police were on the scene and the shooting ended.
At 9:40 police and SWAT teams can be seen from news copters already swarming around the building.
It started and ended in a mere 5 minutes.
The only thing that would have helped is if someone had had a weapon and kept him pinned down and busy for those 5 minutes until the police arrived.
“It started and ended in a mere 5 minutes.”
From the CNN Website:
Police and other first responders arrived on scene about 20 minutes after the first calls.
Police report that no law enforcement officers discharged their weapons at any point.
The gunman took his own life, police said. He took out a handgun and shot himself in a classroom as law enforcement officers approached, officials said.
http://www.cnn.com/interactive/2012/12/us/sandy-hook-timeline/index.html