An inspector posing as an intruder managed to get into a school cafeteria during a security test at a campus in Uvalde, officials say.
A gunman killed 19 children and two teachers when he walked into an elementary school in the Texas city in May and opened fire in a classroom.
Uvalde Consolidated Independent School District interim Superintendent Gary Patterson revealed the findings of the “intruder selection audit” during a school board meeting on Monday.
Mr Patterson told the meeting that the inspector gained access through an unsecured exterior door as a truck was making a delivery in the school building’s loading dock.
The “intruder” pulled on the door and it opened as it had not been closed hard enough. They were able to get into the cafeteria where they were confronted and stopped by staff.
No students were in the cafeteria at the time of the test.
“That really is 100 per cent my responsibility to see that didn’t happen,” Mr Patterson said, according to NBC News.
“The delivery of goods into loading docks was just something, quite honestly, that I overlooked. But I won’t overlook it next time.”
The security check was carried out as part of a statewide programme to randomly check protocols at schools in the wake of the mass shooting at Robb Elementary.
“Overall, you know, not as successful as we had liked, but we are making progress,” added Mr Patterson.
He said that loading area doors would be checked and staff would be given additional training before classes resume in the school district in January.