A Robb Elementary School exterior door did not lock after it was shut by a teacher, shortly before a gunman entered and killed 19 students and two teachers. State police stated Tuesday that investigators are still trying to figure out why.

Initial reports by the state police stated that a teacher had opened the door shortly before Salvador Ramos (18) entered the Uvalde school in Texas on May 24.

According to Travis Considine, chief communication officer at the Texas Department of Public Safety, they have determined that the teacher propped the door open using a rock. However, she then took the rock out and closed the door after realizing there was a shooter. Considine stated that the door didn’t lock.

“We checked that she had closed the door. The door didn’t lock. Considine stated that we now know this and investigators are investigating why the door did not lock.

Additional video footage taken by investigators since Friday’s news conference, when authorities stated that the door was open, confirmed this detail. The door was not propped open by authorities at the time.

Considine stated that Ramos initially propped the door open, but Considine ran inside to grab her phone and dial 911.

Considine stated that she came back out after using her phone and heard someone shout, “He has a gun!” She saw him leap the fence and realized he had one, so she ran inside, taking the rock as she went.

Don Flanary, a San Antonio attorney, told the San Antonio Express-News the Robb Elementary School employee (whom he is not naming) closed the door after realizing there was a gunman on the loose. The attorney stated that she had originally propped the door open to transport food from her car to her classroom.

“She kicked away the rock when she returned in.” Flanary said that she recalled closing the door while telling 911 that he was shooting.

Flanary stated that she believed the door would lock, as it is supposed to always be locked.

Flanary did no immediate return phone messages from The Associated Press.

Investigators are still trying to interview Pete Arredondo from Uvalde Consolidated Independent Schools District Police, who state police claim was the commander of the school shooting scene.

Steven McCraw, Texas Department of Public Safety’s head, stated that Arredondo treated active scene like a hostage situation, and that children were not at risk. Meanwhile, 19 officers waited outside Ramos’ classroom in the school hallway.

McCraw called it the “wrong choice” and stated that the focus of the investigation had shifted to Arredondo’s response.

Considine stated that other officers from the Uvalde and schools police departments continue their interviews and statements. However, Arredondo hasn’t responded to DPS requests since two days.