The initial response appears to have diverged from guidance widely implemented since the 1999 massacre at Columbine High School in Colorado, which says officers should pursue shooters inside buildings without waiting for specialised backup.
According to the Texas Police Chiefs Association’s own policy manual “the first two to five responding officers should form a single team and enter the structure”.
Emergency response experts said quicker action may have limited the slaughter, or could have meant getting the injured lifesaving treatment before it was too late.
Police also revealed that Ramos was able to march into the school unobstructed through a door that had been propped open by a teacher before he fired more than 100 rounds in the attack.
It emerged that the teenage shooter had asked his older sister to buy him a gun a year before the attack, when he was 17.
The TDPS said 60 gun magazines were found at Robb Elementary and 315 spent rounds inside the classroom where 19 students and two teachers were shot dead.
It came as horrifying details emerged from survivors of the massacre.
One schoolgirl recalled how Ramos “backed the teacher into the classroom … looked her right in the eye, and said ‘Goodnight’, and then shot her and killed her”.
Miah Cerrillo, 11, told how she smeared the blood of a classmate over her pretending to be dead in case the shooter re-entered her fourth grade classroom.
In a video, parents at what is apparently the rear of the school building, complain angrily that police are doing nothing as the country’s worst school shooting in a decade unfolds.
Angeli Rose Gomez, whose children were inside, told The Wall Street Journal she was handcuffed by federal marshals after she and others pushed police to intervene.
And an off-duty Border Patrol agent, whose wife taught at the school and whose child attended it, rushed to the scene mid-haircut with a shotgun he borrowed from his barber after his wife texted him from a classroom: “There’s an active shooter. Help.”