Hey there, Shankar here. We're working on a bunch of new episodes coming your way beginning next week.

In the meantime, we wanted to highlight an episode from last June that was a result of many months of research and reporting.

Please note, it includes the sounds of shootings from a college campus, as well as music with violent and explicit language.

If you're listening with small kids, you may want to save this one for later.

This is Hidden Brain, I'm Shankar Vedantan.

On a chilly April morning in 2007, a nightmare unfolded on a college campus in Virginia, a 23-year-old student acting alone, open fire in a dormitory.

He shot and killed two students. Then he walked across campus and began killing people in an engineering building.

The sound of gunfire was caught on a student's cell phone.

We weren't sure what it was. It was gunshots, but for a while we thought it would have been construction. We heard this horrible scream and laughter.

Tina Harrison was a student in the building.

We're sitting in the classroom and basically panic broke out. All we could hear was people screaming, laughter and more screaming.

I counted 24 gunshots within a minute and I lost track after that. I just started praying.

By the time the assault ended, 32 people were dead. The gunmen took his own life.

The shooting at Virginia Tech was quickly seared into our minds as one of the deadliest mass shootings in US history.

Unfortunately, it's been followed by many other school shootings, including the killing of 17 students in Parkland, Florida.

In all these cases, the news media has struggled to convey the sheer scale of the massacre.

There is terror and then sorrow today at the campus of Virginia Tech.

It's an act of evil on a scale that we've never seen in this country before.

Four hours after the news began to break, Blacksburg, Virginia is still in shock from its wounds and so is much of the time.

But even as the country mourned, people began to ask why campus officials hadn't been more proactive.

Why hadn't they spotted the warning signs? Why hadn't they locked down the school after the first shooting of the dorm?

At a press conference, campus police tried to explain.

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