(CNN) -- Robin Dehaven usually replaces windows. On Thursday morning, after a small plane crashed into an Austin, Texas, office building, he was breaking them, having rushed into the burning structure to help people escape.
Dehaven, an Army veteran who works for a glass company, was driving to a job when he witnessed the plane crash. With the building in flames and emergency personnel still minutes away, Dehaven drove his truck to the parking lot.
People in the building were trapped, screaming for help.
"[Other people who'd gathered] said they needed my ladders on my truck, because there were people stuck on the second floor," Dehaven told CNN's "The Situation Room."
He took a ladder off his truck and put it up to a window of a smoke-filled area where five people were trapped.
"The people were kind of in a panic, wanting to get out quickly, of course, so I climbed up into the building with them," Dehaven said. He then broke a nearby window under which the ladder could have better footing, and he helped the five escape, he said.
Dehaven was one of several people who rushed to the site to help, local reports and the Texas governor's office said.
"In true Texas form, first responders and everyday citizens responded to today's plane crash with selfless acts of heroism, securing the area, evacuating the building and controlling the fire, and are to be commended," Texas Gov. Rick Perry said in a written statement Thursday.
Authorities said they believe pilot Joseph Andrew Stack III, 53, of Austin, intentionally crashed the small aircraft into the building, where nearly 200 Internal Revenue Service employees worked. Authorities said Stack apparently had a grudge against the IRS.
The remains of two people were found in the building after the crash, and 13 other people were injured -- one seriously -- authorities said. The identities of the dead weren't released as of Thursday evening.
Witnesses described a scene of panic, fire and smoke. Lyric Olivarez, who was working in a nearby building, told CNN affiliate KXAN that she felt her building shake when the plane crashed.
"It sounded like an explosion, but it felt like an earthquake," Olivarez said. "Someone came into our office and said there was a bomb in the building next door. We had no idea it was a plane at the time."
When she and others ran outside, they saw the neighboring building in flames.
"People on the second and third floors were busting out windows, screaming, 'Help me! Help me! Get me out of here!' waving handkerchiefs or whatever they could find," Olivarez told KXAN.
"Not before long, the entire parking lot was filled with smoke, and people praying and crying," she said.
"I just saw smoke and flames," said CNN iReporter Mike Ernest. "I could not believe what I was seeing. It was just smoke and flames everywhere."
Dehaven said that as he was driving before the crash, he could see the plane flying low, approaching the building.
"I saw it turn and start heading down like it was diving to come in for a landing, but there's no landing [strip]," he said. "So I knew it was going to crash."
He said his 6½ years in the Army, with two tours in Iraq, helped him Thursday.
"I've had some experience in triage and battlefield, with ... gunfire," he said. "My first thought [was] maybe I can help, because I'm more used to dealing with traumatic situations like that.
"I have a clear head and a calm head to try to help those people, and luckily I did."