Chicago (CBS) -- Greg Zanis, a retired carpenter, placed five white crosses outside the Henry Pratt Company Saturday.
The crosses bear the names of those killed in Friday's workplace massacre.
"I'm in denial. It's the hardest thing to do," Zanis said.
Over the past 20 years, Zanis estimates he's delivered more than 20,000 crosses to remember shooting victims including those in Newtown, Connecticut; Las Vegas and Parkland, Florida.
for more features.