It's been a year since 19 fourth graders and their two teachers were fatally shot inside Robb Elementary School in Uvalde, Texas, just two days before the summer break they had been eagerly awaiting.

Among the children were aspiring lawyers, biologists, police officers, dancers. One girl had just celebrated her first Communion. Another was preparing for her 10th birthday.

In the days after their killings, officials gave shifting and contradictory narratives about the chaotic police response that saw dozens of officers waiting in the school's hallway while the gunman roamed two conjoined classrooms with dead, injured and terrified victims. Law enforcement breached the classroom and killed him more than an hour after the massacre began.

Despite officials' promises for thorough probes and accountability, there's still a lot we don't know. Interviews with survivors, preliminary reports and surveillance videos have unveiled the horror that unfolded in the school. But many parents still know little about what their child's last moments were like -- and if their loved one could have been saved during the more than 70 minutes of police inaction.

"If we can find the mistakes that we made, perhaps we can keep it from happening to some other community," Uvalde Mayor Don McLaughlin recently told CNN's Shimon Prokupecz in an interview. He has been calling on state investigators to publicly release records related to the attack. "We can't start healing and get closure till we get answers."

These are five key questions that remain unanswered.

Who is to blame for the botched police response?

Early assessments into the attack highlighted a series of failures from the multiple agencies on scene. In total, 376 law enforcement officers from 23 agencies -- including the US Border Patrol, the Texas Department of Public Safety (DPS) and the local police department -- responded to the massacre.

In June 2022, DPS Director Col. Steven McCraw called the botched police response an "abject failure," adding there "was a sufficient number of armed officers" to confront the gunman about three minutes after he entered the school. Instead, the shooter was confronted roughly an hour and 14 minutes later.

Three local police officers were the first to enter the school after the shooter. They were armed with two rifles, according to a timeline shared by McCraw in June.

McCraw has blamed the incident commander -- Uvalde schools Police Chief Pedro "Pete" Arredondo -- for the delay. Arredondo, who was fired from his position in August, told investigators he was more concerned about saving students in other classrooms than trying to stop a gunman who had already shot children and teachers. But he has said he did not consider himself the incident commander on May 24, 2022.

Arredondo declined to comment for a recent CNN documentary about the attack.

Surveillance footage, first published by the Austin American-Statesman newspaper and obtained by CNN, shows the first officers who approached the classroom doors retreated after the shooter opened fire on them from inside. As time went on, crowds of officers amassed in the hallway, some armed with rifles and ballistic shields. The delay contradicted widely taught active shooter protocol that says officers should act as quickly as possible to stop the threat.

A 77-page interim report released in July by a Texas House investigative committee described an "overall lackadaisical approach" by law enforcement agencies who were at the scene. In that report, Arredondo said he only acted as a responding police officer.

Law enforcement experts have stressed regardless of who was in charge, every officer on the scene had a duty to act.

"I believe that the training is very clear on what we are supposed to do," North Richland Hills, Texas, Police Department Chief Jimmy Perdue told CNN last year. "Even a single officer has the responsibility to go stop the killing. And that did not happen."

Could more victims have survived if authorities confronted the gunman earlier?

Experts believe the delayed police response may have cost lives. Victims' parents -- who still know little about what their loved ones' last moments were like -- wonder the same.

Kim Rubio, who lost her daughter Lexi in the massacre, told CNN in a recent interview she feels robbed of answers from authorities.

"Had they engaged immediately and my child is deceased, then I know in my heart that she wasn't scared very long. But because they waited so long, now I'll never know. I don't know if it was fast and I don't know if it took 30, 40 minutes," she said. "That's hard to sit with."

Survivors have shared stories that show more people may have been alive today if the gunman had been stopped earlier. Fourth-grader Khloie Torres, who called 911 from inside the classroom begging for help, told dispatchers her teacher, Eva Mireles, had been shot but was still alive. Mireles had also called her husband, who was a school district police officer, after she was shot to tell him she was dying.

Mireles was still alive when authorities carried her out of the classroom but had lost a lot of blood.

Noah Orona, who was 10 years old last May and was shot in the back but survived, recalled hearing an unidentified little girl near him "gurgling because she was trying to breathe" after getting shot, his mother previously told CNN.

Another boy who survived remembered the children inside the classroom were asked by police to call out for help if they needed it. But a girl who did just that caught the attention of the gunman, who then shot her dead.

Will anyone be held accountable?

Of the nearly 400 officers who responded to the scene, only a handful have faced employment consequences, including Arredondo.

Seven DPS officers went under investigation for their response to the shooting, the agency told CNN in an email. Two were "served with employment discharge notifications, one was served with a formal written reprimand and the remaining four were closed without sustained findings," the email said.

Among them was Texas Ranger Christopher Ryan Kindell, who was given a preliminary notice of termination in January but remains suspended with pay while awaiting a meeting with the DPS head, the agency told CNN in an email. Kindell arrived at the school that day around noon, roughly 50 minutes before the gunman was killed, and told investigators his actions at the scene "were minimal," sources previously told CNN. In an email to CNN, Kindell said department policies prohibit him from publicly commenting. Sgt. Juan Maldonado, a Texas state trooper, was also served termination papers by DPS in October. But he was instead allowed to retire, DPS confirmed to CNN via email. CNN reached out to him but has not heard back. In an interview with local station KXAN that published in January, Maldonado said he was not given a specific role in the shooting response, and instead worked to save and provide medical care to as many children as he could. Capt. Joel Betancourt, who was investigated by DPS after trying to delay the classroom breach, remains employed with the agency, DPS said. CNN reached out to Betancourt but has not heard back. State trooper Crimson Elizondo also responded to the school attack and was later hired by the Uvalde school district. After CNN identified her as one of the DPS officers under investigation for her actions that day, the school district announced her termination. The district then also suspended its entire police force, citing "recent developments" that "uncovered additional concerns with department operations." CNN reached out to Elizondo but has not heard back. Lt. Mariano Pargas, the acting Uvalde police chief on the day of the mass shooting, resigned from the department in November, days after a CNN report found he knew there were several children alive who needed to be rescued from inside the classrooms but did not take action. Pargas still serves in elected office as a county commissioner. He denies wrongdoing but says he won't talk about the incident.

CNN also asked the Uvalde Police Department about five city officers who were among the first to respond to the shooting, and a city spokesperson confirmed all five are still employed with the department. An internal affairs investigation is still ongoing, city spokesperson Gina Eisenberg told CNN in an email.

McCraw, the head of DPS, has not stepped down despite repeated calls from grieving family members demanding his resignation and a pledge he made to CNN that he would leave if the department was found culpable. McCraw recently declined to sit with CNN for an interview, citing an ongoing investigation.

Uvalde County Sheriff Ruben Nolasco, who was elected in 2020 and who CNN has reported did not appear to have completed an active shooter training course at the time of the massacre, is still at his post. Community members called for his ouster in the aftermath of the attack after he chose to stay at a different crime scene that was already under control while the school shooting unfolded. CNN has reached out to Nolasco and left a message with his office but has not heard back. He previously told CNN he believes his response to the shooting was adequate.

Uvalde County District Attorney Christina Mitchell has said she will charge anyone who has committed a crime at Robb Elementary, including law enforcement officers. To date, no one has been charged.

What has not been released?

A year on, there has not been any official release of any unedited evidence in the case. The investigative committee's July report largely lacked to-the-second timestamps that could help better evaluate the police response. Transcripts of testimony quoted in the report also were not released.

An initial Texas Rangers report into the massacre was completed and turned over to the DA at the end of 2022, an agency spokesperson told CNN.

But the agency has not publicly released any reports and does not plan to until the prosecutor has "had an opportunity to thoroughly review it and make prosecutorial decisions," DPS spokesperson Ericka Miller told CNN.

(More than a dozen major news organizations, including CNN, have sued DPS to obtain records related to the massacre.)

McLaughlin, Uvalde's mayor, has repeatedly criticized the lack of transparency in how Texas authorities have handled the investigation, claiming he's been left in the dark about the probe.

"We as a community need to know what every one of our officers did that day. We still don't know that," he told CNN's Prokupecz. "A year later, we don't know that."

"Part of me wants to say, are we going to uncover something you don't want us to see?"

The city of Uvalde sued the DA last year, alleging she is blocking the city's independent investigator from accessing key evidence relating to the attack. The city has sought access to all body camera footage from the various law enforcement agencies who entered the school, surveillance videos and statements given to investigators, according to the lawsuit.

The victims' autopsy reports were also sealed by a judge after prosecutors argued they contained information that is "vital to the investigation, apprehension and potential prosecution of individuals that may be criminally responsible."

What's next?

Mitchell has said the criminal investigation into potential charges could take years.

Since DPS handed over their preliminary report, the DA has not shared an updated estimate on how long her office's review into the case may take, and when -- or whether -- she expects to present it to a grand jury. She has said the release of any information about the law enforcement response would hurt her criminal probe.

CNN has reached out to her office for an update.

Meanwhile, a separate investigation by the US Department of Justice that launched at the request of Uvalde's mayor is ongoing and has so far included more than 200 interviews, CNN reported last month.

The justice department has not yet set a date for when the findings will be released but said in April it will be in the "coming months."