By Siafa Lewis

PHILADELPHIA (CBS) — There are new questions about the timeline of the school shooting that killed 19 children and two teachers at a Texas elementary school. On Sunday, President Joe Biden and the first lady will travel to Uvalde to console families and honor the victims.

Investigators say the gunman walked into the school through an unlocked side door to carry out Tuesday’s carnage. Troubling details are emerging about the police response to the shooting.

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Two full days have passed since an 18-year-old Texan turned ruthless killer upended countless lives, disturbing the peace in a tranquil community and once again reminding us all of America’s unrelenting scourge of gun violence.

On Thursday, Texas Department of Public Safety Director Victor Escalon briefed reporters on the latest findings of the state’s investigation into the shooting.

“From the grandmother’s house to the [ditch], to the school, into the school, he was not confronted by anybody,” Escalon said.

Previous statements indicated that the shooter had been confronted by officers before he found his way to the fourth-grade classroom where he shot and killed 21.

Former deputy commissioner with the Philadelphia Police Department Joe Sullivan spoke to CBS3 about his training, the many questions he still has as this case unfolds and ideas about preventing future massacres.

“First officer or officers on scene and move immediately. They go to the sound of the gunfire, they engage with the person or persons firing a weapon,” Sullivan said.

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On paper, the thought that the shooter was able to barricade himself in a classroom without any law enforcement intervention for upwards of an hour is troubling, to say the least, but we still don’t know all the facts.

“I understand that there was difficulty getting into the classroom. So that’s why there’s a whole lot of questions that have to be answered,” Sullivan said.

Questions about who was in charge, clear active shooter policies, resources and equipment, training and so much more. In time, we’ll hopefully get those answers but that doesn’t much address prevent the next such shooter.

“They were posting things on social media. This keeps happening,” Sullivan said.

We didn’t discuss a cure-all but Sullivan finds the status quo untenable.

“If an individual has made a decision that he’s gonna harm a bunch of people, he or she is going to find a way to do it. What we need to do is put up as many roadblocks as possible,” Sullivan said.

He believes there are conversations to be had and solutions to be found.

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“The extremism in our country is destroying us from the inside out. You have one side that wants to take everyone’s guns away and that’s never going to happen. And then you’ve got the other side that doesn’t even want to entertain any discussion regarding any type of gun legislation,” Sullivan said.