Yes, I think they are in CYA mode. Notice how the journalist who wrote the story tries to address this question saying police were trying to figure out if there were multiple shooters. What difference does that make? I know there would be a lot confusion during such an incident, but all current active shooter response scenarios now say police are supposed to go towards the shooter immediately.
Here is the police dispatch to compare to the 911 calls:
http://nhregister.com/articles/2012/12/14/news/doc50cc0897adc1a203744261.txt?viewmode=default
Same with the cops claiming the school had been cleared within moments after they did enter. Then they set up HQ in the office mere inches from where the nurse and secretary were hiding for hours. No way did they clear it and no way did they ever look for a second shooter.