It was lunchtime in San Bruno, California, on Tuesday when a restaurant owner heard what sounded like construction.
"First it came out slow -- 'pop pop' -- then it was fast," Denny, owner of Hashes & Brews, told ABC News.
The sound turned out to be gunshots.
Next, Denny, who did not want to provide his last name, said he saw people running out of the nearby YouTube building.
"I saw one was bleeding in the face," he said. "I told him to come inside the restaurant."
Denny thought it was another mass shooting.
"Out of the three people that came up to me first, one was wounded in the ankle, one was bleeding in the face," he said. "I took them inside the restaurant, I gave them waters, gauze, towels ... just trying to help out the situation as much I could."
He said the woman with a wound to her ankle had a bullet lodged in her shoe.
"They just were in shock," Denny said. "They were shaking, they made me shake because it's just a terrifying situation."
Denny was scared but he said he left the victims inside "and went back outside just to make sure nobody was coming down the street this way with a gun, because you never know. You don't know what their motive was. Obviously, three people I saw, two of them were bleeding."
The suspect, Nasim Aghdam, shot and injured several people at the YouTube building Tuesday afternoon before fatally shooting herself, according to police. Four victims were hospitalized, three with gunshot wounds and one with an ankle injury from running away from the scene.
For Denny, the reality sank in as police and ambulances swarmed at the scene.
"It's sad. Because you hear about it in the movies, in TV, but you don't see it in your front yard," he said. "You never think it'll happen here. But, then again, you never think it'll happen inside a church or inside a school."