Newtown 911 calls: Calm, anguish as massacre unfolded (AUDIO)

The 911 calls from last year's Newtown school shooting released Wednesday reveal a mixture of calm and anguish among callers as the massacre unfolded.

The first call came from a woman inside Sandy Hook Elementary School.

"Sandy Hook school," she says. "I think there's somebody shooting in here. In Sandy Hook school."

"OK, what makes you think that?" the dispatcher asks.

"Because somebody has a gun. I saw a glimpse of somebody running down the hallway."

"OK ..."

"They're still running, they're still shooting," the caller yells. "Sandy Hook school please!"

The calls were posted on the town's website under a court order after The Associated Press challenged local authorities' refusal to publicize them.

Dispatchers are heard calmly responding to tense calls by school staff members and nearby residents. Many are told to take cover.

Gunfire is heard in at least two of the calls.

"I keep hearing shooting," Sandy Hook's custodian says in one call. "I keep hearing popping!"

The shooter, 20-year-old Adam Lanza, shot his mother to death before driving to the school on Dec. 14, 2012, and gunning down 20 first-graders and six adults before turning the gun on himself.

Last week, investigators released a report on the Newtown massacre that concluded Lanza had acted alone, and that his motivation for the attack "may never be answered."