When the first shot rang out, Brian Dillon left the loading dock at the Empire State Building to investigate. He saw a man in a suit shoot another man four times in the head, then walk away.
Others might have frozen or fled. Dillon followed.
When he saw police, the construction foreman started screaming, "Get the guy in the gray suit! He just murdered somebody!"
Moments later, the officers opened fire, killing the gunman, Jeffrey Johnson, and wounding nine bystanders.
City officials said Dillon's actions, coupled with a swift police response, likely saved lives Friday. Mayor Michael Bloomberg called Dillon a hero.
"He saw something, he said something," Bloomberg said.
Dillon, 44, reached at his Tuckahoe home Saturday night, said he didn't have time to think about what he should do: "I just reacted."
A foreman at the work site since January, Dillon said his colleagues yelled at him to stop when he heard the gunshot and headed that direction. He said he got a good look at the gunman's face after he fired the final shots, describing it as expressionless.
"He was doing a job, and he knew what he was doing. Then he just spun around with his briefcase in his left hand, the gun in his right, and walked east down the south side of 33rd Street," Dillon said.
As a pair of police officers heard Dillon's calls for help and began closing in on Johnson, the shooter raised his gun.
"He spun around with the gun in his hand coming up to shoot, is what it looked like," Dillon recalled.
He doesn't think Johnson ever looked straight at him, but at that moment he was scared. "I didn't want to die," he said. "I wanted to go home."
Seconds later, the officers opened fire on the busy sidewalk as people ran for their lives.
Looking back on the chaos a day later, Dillon said getting involved was the right thing to do. "There are some things in life you just got to do, you know?" he said.