December 23, 2012 10:25 AM CBSNewYork

Some of the emergency officials who responded to 911 calls from the Sandy Hook Elementary School on the day of the shooting massacre are opening up about the tragedy they faced that day.

“You could hear it in their voice, and that’s I think part of how everybody knew that was working that day that this was more than just a routine call,” said Newtown patrol officer Liam Searbrook.

The first 911 call came in around 9:30 a.m., when shooter Adam Lanza began opening fire inside a classroom.

“Approaching the scene, there were approximately six children that were running from the scene which added to our knowledge that yes, this is real,” Newtown Police Sgt. Dave Kulgren told CBS 2’s Teresa Garcia.

First responders arrived within minutes of the 911 calls that came in the morning of December 14th. Officers said they broke windows to get inside to search for the shooter.

“We heard gunfire and we just went towards it,” Kulgren said.

In the minutes it took place to respond, Lanza fired enough shots to kill 20 first graders and other faculty at the elementary school.

Investigators said that Lanza shot himself in the head when he heard police coming.

“I walked in and it was horrific, the crime scene itself. And to see the adults and the children that were deceased in the classrooms, it was very hard, obviously, to comprehend what had happened,” Newtown Police Captain Joe Rios said.

“I was devastated, absolutely devastated. I had no words,” Police Chief Michael Kehoe said. “You feel a sense of guilt that you weren’t there quick enough to do that, but also I know our response stopped hat threat…and he could not proceed any further.”