•Witnesses have described traumatised children covered in blood being hugged by parents. Others had to come to terms with the devastating news of the deaths of loved ones.
•But Tuesday began much like any other weekday in May in Uvalde, about 80 miles (130km) west of San Antonio.
As the US reels from another school shooting, more details are emerging of the horror that unfolded in Texas near the border with Mexico.
Witnesses have described traumatised children covered in blood being hugged by parents. Others had to come to terms with devastating news of the deaths of loved ones.
But Tuesday began much like any other weekday in May in Uvalde, about 80 miles (130km) west of San Antonio.
Around 08:00 local time, near the centre of the town, some 600 students aged seven to 10 were arriving at Robb Elementary School.
The summer holidays were fast approaching and many children were savouring their final days in middle school before graduation.
How the shooting began
That morning on the other side of town Salvador Ramos fired the opening shots of one of America's deadliest mass shootings.
Described as a loner, from a "fraught home life", and bullied over a speech impediment - the 18-year-old shot his grandmother before fleeing the scene in a battered truck carrying guns and copious ammunition.
According to CBS News, Ramos' grandmother, who is in a critical condition, was only discovered after the shooting when officers arrived at her home to investigate.
After driving erratically across town Ramos eventually crashed his car into a ditch near Robb Elementary School at around 11:30am, police said. Some bystanders approached the car to offer assistance.
"People thought that he was in trouble and so they jumped out to help him and he came out of his vehicle and started shooting at them," one person told the Spanish language network Telemundo.
A police officer who works at the school and then two officers from the Uvalde police department all fired at Ramos - but they could not stop him and instead called for back-up, Eric Estrada from the Texas department of public safety told CNN.
Video shared on social media showed a person clad in black jogging toward a side door of the school carrying what appeared to be a rifle.
Texas Department of Public Safety spokesperson Chris Olivarez told CNN that Ramos then forced his way into a fourth-grade classroom.
As police arrived at the scene, Ramos barricaded himself in the classroom and prepared for a showdown with law enforcement officials.
It was there that children were "shot and killed horrifically, incomprehensibly", according to Texas Governor Greg Abbott.
All 21 victims of the shooting were later found in the room.
The gunman was in the school for roughly one hour, police said.
Ramos is believed to have purchased two semi-automatic rifles immediately after turning 18 last week.
Witnesses reported seeing children clambering out of nearby windows and seeking shelter at a funeral home nearby as the shooting began.
Others, led by two teachers, escaped from the building and hid behind some trees at the rear of the school.
Marcela Cabralez, a local pastor, told the Washington Post that her nine-year-old granddaughter was eating her lunch with other students when she heard noise coming from outside, including shots and breaking glass.
Teachers shepherded children behind a curtain, where they all hid, desperately trying to avoid attracting the shooter's attention. Ms Cabralez's granddaughter hid in a bathroom.
Another teacher, Eva Mireles, was shot and killed by the gunman while trying to protect her students.
Adolfo Hernandez told the New York Times that his nephew had been in a classroom near where the shooting had taken place.
"He actually witnessed his little friend get shot in the face," Mr Hernandez said. The friend, he said, "got shot in the nose and he just went down, and my nephew was devastated".
Travis Considine, a spokesman for the Texas Department of Public Safety, told reporters that two police officers were injured after after exchange of fire with Ramos.
The massacre finally came to an end shortly after 13:00, when a nearby Border Patrol officer shot Ramos in the head. State officials said officers had contained the gunman inside adjoining classrooms, and eventually were able to breach the room he was in.
Seven 30-round magazines belonging to the teenager were later found at the school.
Children were rushed to a local community centre about a mile from the school and Mr Sotelo said he saw several teachers and children emerging sobbing and injured.
"We saw a little girl full of blood and the parents were screaming, it was an ugly scene," Derek Sotelo, a resident who runs a local auto-repair shop shop, told the Washington Post. "They were just little kids."
'Don't take a second for granted'
As police began investigating, a frantic scene was emerging at the school as parents arrived seeking news.
Journalists at the scene reported hearing cries and sobs as family members who gathered there received the devastating news that their children had been killed.
Angel Garza wrote on Facebook that his 10-year old daughter Amerie had been killed.
"My little love is now flying high with the angels above. Please don't take a second for granted. Hug your family. Tell them you love them," he wrote on Facebook.
And Lisa Garter mourned the death of her 10-year-old son Xavier Javier Lopez.
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"He was just a loving 10-year-old little boy, just enjoying life, not knowing that this tragedy was going to happen today," she said.
Others, left in limbo by the chaos surrounding the events, were asked to give DNA samples to help identify some of the young victims.
Jesse Rodriguez told the San Antonio Express that he was still waiting for information about his daughter after hearing she could have been taken to hospital.
"I was waiting for more info. Nobody called me back," he said. "The hospital's closing me out right now."
'Why do we keep letting this happen'
As news of the shooting filtered through to Washington, a familiar spectacle unfolded.
President Joe Biden, who once stood with Barack Obama as his predecessor wept in the wake of the 2012 Sandy Hook shooting, raged against legislators' failure to take action.
"Why do we keep letting this happen?" Mr Biden asked in a speech at the White House. "Why are we willing to live with this carnage?"
Accompanied by his wife, Jill, Mr Biden recalled the loss of his own son, Beau, as he empathised with the parents who he said "will never be the same".
"To lose a child, it's like having a piece of your soul ripped away," he said.
IMAGE SOURCE,GETTY IMAGESImage caption,Uvalde residents gathered for a vigil on Tuesday evening
But in the Senate, some politicians remained unswayed by arguments for more gun control.
Texas Senator Ted Cruz accused Democrats and the media of "politicising" mass shootings, while others simply offered "thoughts and prayers".
Another Republican, Texas Attorney General Ken Paxton, urged states to arm teachers and "potentially other administrators".
'You can't comprehend evil like this'
Later, as night fell in Uvalde, police stood watch in the pouring rain outside a community centre where families had earlier gathered to seek news of their loved ones.
Just blocks away, a small vigil was taking place.
Karla Bohman's voice cracked as she told the group about a family friend whose young daughter, a student at the school, was among those still unaccounted for.
"They don't know if she's in surgery or one of the fatalities, but they know she's a victim of some sort because she's missing," Bohman cried. "I can't believe this."
Cheryl Juhasz, a lifelong resident of Uvalde, quietly wept during the prayer.
"You can't comprehend evil like this. No matter where it happens, but it's harder when it happens at home."
The gunman had given scant warning of the horror he perpetrated.
He sent three short social media messages minutes before the massacre, the last of them reading, "I'm going to shoot an elementary school", Gov Abbott said on Wednesday.