Police might have assumed the door was locked, but the latest evidence suggests it may have been open the whole time, possibly due to a malfunction, the source said.
The surveillance footage indicates gunman Salvador Ramos, 18, was able to open the door to classroom 111 and enter with an assault-style rifle, the source said.
Police finally opened the door to classroom 111 and killed Ramos at 12:50 p.m.
Footage shows that Ramos fired rounds inside classrooms 111 and 112, briefly exited into the hallway and then re-entered through the door, the source said.
He said he held officers back from the door to the classrooms for 40 minutes to avoid gunfire.
Days after the shooting, DPS said the exterior door that Ramos entered had been left propped open by a teacher.
State Rep. Roland Gutierrez, D-San Antonio, whose district encompasses Uvalde, said he was unaware of the revelations about the door. »