A teacher who authorities initially believed propped open a door at Robb Elementary School that gunman Salvador Ramos used to enter actually closed the door shut, but it didn’t lock, state police revealed Tuesday.

Investigators say the teacher removed the rock she used to prop the door open, but then closed it when she saw the 18-year-old shooter crash the truck he was driving, said Travis Considine, chief communications officer for the Texas Department of Public Safety.

But the teacher didn’t know the door didn’t lock behind her, Considine said.

“She came back out while on her phone, she heard someone yell, ‘He has a gun!’, she saw him jump the fence and that he had a gun, so she ran back inside,” once she removed the rock, Considine said.

“We did verify she closed the door. The door did not lock. We know that much and now investigators are looking into why it did not lock.”

Ramos shot his grandmother in the face before he stole her truck and crashed it near the school where he shot and killed 19 children and two teachers.

The latest detail in the lead-up to one of the worst school shootings in American history was confirmed through additional video footage reviewed since last Friday when officials at a press conference said the door was left open by a teacher.

The teacher has not been identified.

San Antonio lawyer Don Flanary told the San Antonio Express-News that the elementary school staffer used a rock to keep the door open at first so she could bring food into the building from a car, but shut the door when she realized a gunman was on the loose.

“She kicked the rock away when she went back in. She remembers pulling the door closed while telling 911 that he was shooting,” Flanary told the newspaper.

“She thought the door would lock because that door is always supposed to be locked.”

With Post Wires