The first images showing armed police waiting in a corridor during last month’s school shooting in Uvalde, Texas have emerged.
Officers arrived earlier in the attack and with more powerful weapons than previously reported, according to US media who have seen investigative documents.
Police have been accused of failing to act quickly enough to stop the attack.
Twenty-one people, including 19 children, died in the shooting.
Texas police have not publicly commented on the reports, from the Austin American-Statesman and KVUE-TV.
More details of 24 May shooting at the Robb Elementary School classroom are expected to be presented at a public hearing in the Texas Senate later on Tuesday.
The attack by an 18-year-old local – identified as Salvador Ramos – has led to renewed national debate about gun regulations.
The Austin American-Statesman and KVUE say the documents, the source of which has not been revealed, show that the gunman entered the school at 11:33 local time.
They say 11 police officers arrived within three minutes, and an officer with a ballistic shield was in the building at 11:52.
This happened after school district police chief Peter Arredondo had reported that the gunman had “shot a lot” and that the police only had “pistols”, according to the media outlets.
The new information shows Mr Arredondo also tried to speak to the gunman, asking him whether he could hear him, the Austin American-Statesman says.
The police finally breached the door into the classroom where the gunman was at 12:50. He was shot dead by members of the US Border Patrol Tactical Unit.
During the attack, children were frantically calling 911 to report multiple gunshot victims. Worried parents also tried to rush in, as police physically prevented them from entering.
Investigators say that messages from the children were not being relayed to the officers at the scene, who were waiting for more firepower to arrive before confronting the rifle-wielding killer.
Officials say the police were “wrong” to think that the situation had changed from an active shooter to a barricaded subject, and that they had more time to prepare their response.
The reported delayed response has been the focus of several investigations on the state and the federal levels.
On Monday, the parents of the victims and other members of the community called for the resignation of Mr Arredondo.