The Houston Chronicle reports that the scores of police who responded to the Uvalde massacre did not try to open the doors of the classrooms where the shooter was killing children and teachers until more than an hour had passed. (The story was originally published in the San Antonio Express News.) The story is based on surveillance video.

When you read the story, you will see why Governor Greg Abbott and Lt. Gov. Dan Patrick are trying to block any public release of official investigations until after the state elections in November. More than 100 “good guys with guns”were unable to stop one bad guy with a gun. The more we learn, the more questions are raised about the training, competence, and courage of those who were supposed to protect the students and teachers.

Surveillance footage shows that police never tried to open a door to two classrooms at Robb Elementary School in Uvalde in the 77 minutes between the time a gunman entered the rooms and massacred 21 people and officers finally breached the door and killed him, according to a law enforcement source close to the investigation.

Investigators believe the 18-year-old gunman who killed 19 children and two teachers at the school on May 24 could not have locked the door to the connected classrooms from the inside, according to the source.

Interactive timeline: Minute-by-minute reconstruction of Uvalde school shooting

All classroom doors at Robb Elementary are designed to lock automatically when they close and can only be locked or unlocked from the outside with a key, the source said. Police might have assumed the door was locked. Yet the surveillance footage suggests gunman Salvador Ramos, 18, was able to open the door to classroom 111 and enter with assault-style rifle — perhaps because the door malfunctioned, the source said.

Another door led to classroom 112.

Ramos entered Robb Elementary at 11:33 a.m. that day through an exterior door that a teacher had pulled shut but that didn’t lock automatically as it was supposed to, indicating another malfunction in door locks at the school.

Police finally breached the door to classroom 111 and killed Ramos at 12:50 p.m. Whether the door was unlocked the entire time remains under investigation.

Regardless, officers had access the entire time to a “halligan” — a crowbar-like tool that could have opened the door to the classrooms even if it was locked, the source said.

Two minutes after Ramos entered the building, three Uvalde police officers chased him inside. 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.

Ramos then shot at the officers through the closed door, grazing two of them with shrapnel. The officers retreated to wait for backup and heavy tactical equipment rather than force their way into the classrooms.

Pedro “Pete” Arredondo, the Uvalde school district police chief and the on-scene incident commander, has said he spent more than an hour in the hallway of the school. He told the Texas Tribune that he called for tactical gear, a sniper and keys to get inside. He said he held officers back from the door to the classrooms for 40 minutes to avoid gunfire.

When a custodian brought a large key ring, Arredondo said he tried dozens of the keys but none worked.

But Arredondo was not trying those keys in the door to classrooms 111 and 112, where Ramos was holed up, according to the law enforcement source. Rather, he was trying to locate a master key by using the various keys on doors to other classrooms nearby, the source said.

While Arredondo waited for a tactical team to arrive, children and teachers inside the classrooms called 911 at least seven times with desperate pleas for help. One of the two teachers who died, Eva Mireles, called her husband by cellphone after she was wounded and lay dying.