Police were urged to charge into a deadly school shooting in Texas by onlookers, witnesses say, with one suggesting he considered doing so himself as he became frustrated.
Texas officials say gunman Salvador Ramos was inside the school in Uvalde for up to an hour before he was killed.
Nineteen children and two adults died, while 17 others were injured.
Eyewitness Juan Carranza told the Associated Press that women shouted at officers to "go in there".
But the 24-year-old, who witnessed the scene at the Robb Elementary School from outside his house, said police did not enter.
Javier Cazares, whose daughter was killed in the attack, told the news agency he suggested running in with other onlookers because the police "weren't doing anything".
Authorities said the gunman locked himself in a classroom which officers then struggled to gain access to.
Steven McCraw, the director of the Texas Department of Public Safety, told a news conference on Wednesday that the gunman was on site for between 40 minutes and an hour before law enforcement were able to "contain" him.
US Border Patrol Chief Raul Ortiz, meanwhile, told CNN that dozens of officers responded to the shooting and "didn't hesitate".
"They entered that classroom and they took care of the situation as quickly as they possibly could," he said.
It has also emerged that the attacker sent messages on social media about the shooting minutes before it happened.
Texas Governor Greg Abbott said Ramos had promised to shoot his grandmother in private messages sent 30 minutes before the attack.
A later message declared he had done so, and in a final one sent 15 minutes before the shooting, he announced he would target an elementary school.
According to CNN, the private messages were sent to a 15-year-old girl in Germany who Ramos had met online.
In a statement, Meta, Facebook's parent company, said the "private one-to-one text messages" were "discovered after the terrible tragedy occurred". It added that it was "closely co-operating" with investigators.
Tuesday's events in Uvalde - an unassuming town some 80 miles (129km) from San Antonio, America's seventh-largest city - brought the discussion around gun control once again to the fore, even as members of the small community sought to make sense of the tragedy.
Many there expressed divided attitudes about guns.
"As a kid, I remember my uncles teaching me and training me on how to hold a gun," Carlos Velasquez, a local resident, told the BBC.
"The juxtaposition of good safety with what just happened is so nuanced. It's not just a clean-cut thought - it's a really sticky situation and sticky conversation to have now," he said.
Others, however, were shocked that Ramos was able to carry out an attack with an AR-15 style semi-automatic rifle.
"This kid was just 18. You have to be 21 to drink. How?" asked Sandra Parra, who lives down the street from the school. "I hope there are changes," she said, referring to gun laws in Texas. "I don't have a gun myself, but if I did, it would be for protection," she added.
It is legal to buy a gun at 18 in Texas, and according to US media, the attacker bought his soon after his birthday.
Described as a loner from a "fraught home life", the gunman shot his grandmother before fleeing the scene in a battered truck carrying firearms and copious ammunition. He then drove erratically across town and crashed his car into a ditch near Robb Elementary School.
An officer engaged with him, but failed to stop him from entering the school. He then proceeded to shoot 19 children and two teachers dead, before officers converged on the classroom and a border patrol officer who had responded while nearby killed him, according to Mr Abbott.
Mr Abbott said there had been no history to suggest the gunman could be a danger apart from the social media messages sent before the killings.
Speaking on Wednesday, US President Joe Biden said the idea that a teenager was able to legally purchase weapons that were "designed and marketed to kill, is just wrong".
"I'm just sick and tired of what's going on and what continues to go on," he said, calling for "action" on gun control.
His comments followed an incident at Mr Abbott's news conference, where the governor's Democratic challenger for office, Beto O'Rourke, heckled the Republican for not doing enough on gun control.
In response, Mr Abbott accused Mr O'Rourke of grandstanding.
According to the Texas Politics Project, only 43% of Texans support stricter gun laws. Nationally, the figure is 53% in support, according to a 2021 Pew Research Center poll.
As more details of the mass shooting emerged, the Uvalde community grieved.
The children killed were aged between seven and 10 years old. Teachers Eva Mireles and Irma Garcia also died in the attack. More than a dozen people were also wounded.
Vigils took place for the victims of the shooting, while people have been laying flowers near the school campus as tributes.
"The normality is not here anymore," Ms Parra said.
"Uvalde will be known for its mass shooting," said Mr Velazquez. "That's really unfortunate."