Composer Steven Sametz has spent the past two years seeking harmony out of deep sorrow.

He is perfecting a special piece of music -- a child's requiem to honor the 26 victims of the Sandy Hook Elementary School shooting. The Lehigh University professor grew up just 20 miles from Newtown, Connecticut.

We first met Sametz in 2013. He wanted to write from a child's perspective, so he reached out to elementary school kids around the country. Many of them have first-hand knowledge of gun violence.

Sametz received nearly 500 stories from kids around the country, some so powerful he wanted to hear them in person.

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"My dad was about to go outside with me, and someone had a gun and shot my dad," Sametz read from a letter from a child.

Last year, he visited a school in Philadelphia. One by one, the children read their real-life stories aloud.

"Eventually, like, they found his body dead inside the park," one child said.

"I lost my 9-year-old cousin because some man shot him four times," said another. "I ... you will never be forgotten."

Eleven-year-old Brianna had three family members murdered.

"My uncle, my aunt and my great-grandmom got shot out of nowhere," Brianna said.

Eleven-year-old Brianna tells composer Steven Sametz how her life has been affected by gun violence. CBS News

Sametz is including some of these children's words, even those who couldn't read them without crying.

Jose, who's also 11, has already witnessed the murder of a friend.

Last week, Jose was on hand with some of his classmates to listen to Sametz's completed work performed by the University of Connecticut Symphony Orchestra and Concert Choir.

And he watched as a member of Chorus Angelicus honored his friend by speaking his words.

"He's my best friend out of like the whole entire world, I would do anything for him," Jose had written. "And he, he was gone."

"We've honored the families of those who lost children," Sametz said. "And now I think what's happening, it's beginning to take a larger scope. That it's becoming about bigger issues about how to keep children safe."