A new wave of anger has swept through Uvalde over surveillance footage of police officers in body armour waiting in the hallway of Robb Elementary School while a gunman fired on children and teachers.

The video published on Tuesday by the Austin American-Statesman is a disturbing 80-minute recording of what has been known for weeks now about one of the deadliest school shootings in US history: Heavily armed police officers, some with rifles and bulletproof shields, massed in the hallway and waited more than an hour before going inside and stopping the massacre.

The mass shooting on May 24 claimed the lives of 19 fourth-grade students and two teachers.

The footage from the hallway, which until now had not surfaced publicly, anguished Uvalde residents anew and redoubled calls in the small South Texas city for accountability and explanations that have been incomplete — and sometimes inaccurate — in the seven weeks since the shooting.

Hours after the video was published, residents at a Uvalde City Council meeting shouted for action and demanded that police face consequences.

The footage from a hallway camera inside the school shows the gunman entering the building with a AR-15 style rifle and includes 911 tape of a teacher screaming, “Get down! Get in your rooms! Get in your rooms!”

Two officers approach the classrooms minutes after the gunman enters, then run back amid the sounds of gunfire.

As the gunman first approaches the classrooms a child down the hallway can be seen poking their head around the corner and then running back while shots ring out.

Later, about 20 minutes before police breach the room, the video shows a man wearing a vest that says “sheriff” use a hand sanitiser dispenser mounted on the wall.

Officials said the 77 minutes of footage they are preparing to release does not contain images of children in the classroom.

Republican politician Dustin Burrows, who is leading the investigation, said after the video was posted by the Statesman that “watching the entire segment of law enforcement’s response, or lack thereof, is also important”.

But the video alone does not answer all the questions that remain nearly two months later about the law enforcement response.

In an interview with The Associated Press, Uvalde Mayor Don McLaughlin said: “This has been the most unprofessional investigation or handling of it that I’ve ever seen in my life.

“These families get blindsided constantly.”