It’s been nearly 11 years since the shooting at Sandy Hook Elementary School that killed 20 first graders and six educators.

Since then, mass shootings have taken many more lives at schools and in communities across the United States.

“It’s about too easy access to too many guns with very little regulations. That’s what it is. That’s what sets us apart,” said Mark Barden, whose son, Daniel, was shot and killed at Sandy Hook.

NPR’s Michel Martin spoke with Barden about a new documentary, “A Father’s Promise,” which chronicles his life as a professional musician before and after Sandy Hook. The movie opens Friday and features music and performances by Sheryl Crow, Bruce Springsteen and others.

Here are some interview excerpts:

On hearing of a lockdown on the day of the Sandy Hook School shooting

I remember thinking, ‘They’re taking a safety precaution for whatever reason.’ And then a neighbor called and said, ‘There was a shooting at Sandy Hook.’ And I was just in motion, flying down to the school where I had been many, many, times as a volunteer.

As more information became available, that maybe there was a shooting inside the school, I immediately started to gear up to, ‘If that’s true, I’m going to have to figure out how to explain that to this beautiful little empath,’ which is our Daniel. And as the day – the morning – went on, the news became more clear. It’s hard now to imagine that Daniel is gone – and gone forever.

Barden says music provided no immediate comfort following the shooting

As a musician, the natural tendency is to think: Well, a devastating tragedy occurred. [Music’s] going to be your solace. And that’s what you’ll turn to for comfort.

I think because all three of my children, James, Natalie and Daniel, are very connected to my music, and Daniel very much so. As a result, I just couldn’t get near music or thinking about playing guitar for quite some time after that.

New documentary provided a place to talk and grieve, but trauma endures, he says

It’s difficult for me to hear myself tell my story, or hear somebody introduce me as the father of a child who was murdered. It’s still hard to comprehend that.

And then to connect it with music – to know that now that my “true self” and my “music self” have been able to merge with the advocacy work that I’ve been doing for the last 11 years. It’s an interesting “worlds collide” moment for me that I think has a lot of potential.

On what Barden’s Sandy Hook Promise fund hopes to accomplish

We did advocate for passing the Manchin-Toomey universal background check bill. When that bill failed, it was kind of a catalyst for us to reexamine that model.

You still have to support and introduce bipartisan school safety, gun safety and mental health [legislation]. But we also learned that there are always warning signs before somebody harms themselves or others.

And those warning signs represent opportunities – for people who are trained – on how to identify them, and have the tools to get that individual connected to the help or the services they need, before it becomes a tragedy.

I think we’re on our sixteenth school shooting prevented from happening by students trained in our “Know the Signs” program. More than 500 suicides didn’t happen because students trained in our “Know the Signs” programs knew how to get themselves the help that they need.

And to get the word out that we have this product that’s working, that doesn’t cost anything. Bringing that through musicians and having them explain to their base – there are solutions available to us.

Gunshot is the number one cause of death for young people under 19 in this country. It should be on everybody’s list of something to be talking about and doing something about.

This interview has been edited for clarity and condensed.