The gunman who attacked a school in Texas on Tuesday was able to enter the building unobstructed, police say.
Texas Ranger Victor Escalon said no armed guard challenged the teenage attacker and it is unclear if the school door was even locked.
Mr. Escalon defended the police response amid mounting criticism of an apparent delay in confronting the gunman.
Witnesses were quoted as saying police were hesitant to confront the killer inside Uvalde’s Robb Elementary School.
The attacker shot dead 19 students and two teachers, and injured at least 17 more people. Further tragedy struck two days later, when the husband of one of the murdered teachers died from a heart attack.
The latest details from police sharply contradict what was said at a news briefing two days ago.
Mr. Escalon said on Thursday that initial reports the gunman had shot a guard were incorrect, and there was in fact no guard inside the school when the shooter arrived.
Mr. Escalon said officers entered the school four minutes after the gunman went in at about 11:40.
But it was an hour before the gunman was killed in a shootout, at 12:45, after US Border Patrol tactical teams arrived.
“They [didn’t] make entry immediately because of the gunfire they were receiving,” Mr Escalon told reporters.
Videos have emerged of police being urged by desperate family members to storm the building immediately.
A father whose daughter died in the attack told the Associated Press news agency he had considered running into the school with bystanders out of frustration at the police response.
One mother told the Wall Street Journal that she was briefly handcuffed, accused of impeding a police investigation, after demanding along with other parents that officers storm the building. Angeli Rose Gomez said she saw one frantic father thrown to the ground by an officer, another father pepper-sprayed and a third who was later tased.
“The police were doing nothing,” said Ms Gomez, who was eventually released before she said she jumped over the school fence and ran inside to rescue her two children. “They [the police] were just standing outside the fence. They weren’t going in there or running anywhere.”
Mr. Escalon – a Texas Ranger and spokesman for the Texas Department of Public Safety – said that during the time officers were outside the school they were calling in reinforcements and “also evacuating students, teachers”.
“An hour later US Border Patrol tactical teams arrive, they make entry and shoot and kill the suspect,” he added.
This deviates from guidance that became standard police practice after the 1999 Columbine High School massacre, which states that the first officers on the scene should do whatever they can, and as fast as they can, to stop an attack, without waiting for backup.
After crashing his truck into a ditch near the school, the gunman emerged and began firing an AR-style rifle at two people who were exiting a funeral home.
The suspect then jumped a fence and began firing “multiple, numerous rounds” at the school building, Mr Escalon said.
As he approached the entrance he “was not confronted by anybody”, the ranger said.
According to Uvalde County Independent School District Officers protocol, campuses are required to have staff “who patrol door entrances, parking lots and perimeters”. Teachers are told to keep doors locked at all times.
“We will find out as much as we can why it was unlocked,” Mr. Escalon said. “Or maybe it was locked. But right now, it appears it was unlocked.”
Texas congressman Joaquin Castro has written to the director of the FBI to ask that agents investigate the law enforcement response to the attack as it was unfolding.