At the scene of some of the nation's worst tragedies — mass shootings and other acts of terror, natural disasters — there has been a constant: handmade white crosses neatly arranged and bearing the names of every victim killed.
It was a memorial project that began in 1996 and was conceived by an Illinois carpenter named Greg Zanis, who told NBC News on Thursday that "it evolved quickly into something I certainly didn't expect to have that great of a need."
Now, Zanis, 69, has decided it's time to retire from the self-appointed role he's held for more than two decades building the crosses (or stars of David or crescent moons depending on the victims' religious affiliation) and transporting them to each scene of violence and loss.
"I just feel like it was a calling only I could have filled," Zanis said, estimating he has built about 27,000 crosses since launching Zanis Crosses for Losses, which has been funded out of his own pocket and through donations.
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Ahead of his decision to step back from his work in November, this year was particularly exhausting, he said.
Then, in August, he drove from the Chicago area to El Paso, Texas, where 22 people were fatally shot at a Walmart. After arriving and setting up the crosses in their honor, he was startled to learn of another mass shooting the next day in Dayton, Ohio, where nine people were killed outside a bar. He immediately drove his pickup more than 1,500 miles to deliver crosses to that scene.
He spoke with NBC's Lester Holt from El Paso about what kept him going: the approval from grieving loved ones.
"This is all they have left," Zanis said at the time, "and I know that and I know it means the world to them."
Zanis said his mission began as a tribute to his own father-in-law who was murdered in 1996.
In the years he has been doing this, he said, his phone rings almost immediately after a mass shooting happens; people look up his name because sometimes they don't know where else to turn.
In many cases, he added, he actually knows the victims' names before officials release them because families and friends reach out to him.
The work, however, has taken an emotional toll on him, and while he tried to stay strong wherever he went, there were moments when he would break down in tears. He hopes his past efforts have given others a sense that they are not alone.
"I saw it as something that makes a difference, and touches families, the city, state and nation," he said.
Joe Studley is an assignment editor for NBC News.
Erik Ortiz is a staff writer for NBC News focusing on racial injustice and social inequality.