Since the day 13 people were killed at Columbine High School in 1999, a carpenter from Illinois has hopped in his pickup truck to deliver 26,274 handmade wooden memorials — mostly crosses, and sometimes Stars of David or crescent moons — across the country, unifying grieving communities after mass shootings, natural disasters and other tragedies.

But this week the carpenter, Greg Zanis, did not have to drive far. After a former employee at an industrial warehouse fatally shot five workers and injured five police officers in suburban Chicago, he ministered to his neighbors by setting up five more crosses.

On Friday afternoon, Mr. Zanis, whom some refer to as the “Cross Man,” watched dozens of police cars drive past the house where he lives with his wife and three of his children in Aurora, Ill. His daughter informed him they were responding to an active shooter.

“It felt like someone had hit me upside the head,” Mr. Zanis said in a phone interview. “I didn’t see it coming.”