(ABC NEWS)- When Secret Service agents Damian Schwartz and Don Vinci walked toward their offices at the World Trade Center on the morning of Sept. 11, 2001, they were unaware they would spend the rest of the day responding to the worst terror attack in U.S. history.
"I just remember it being a beautiful day, the sky was as blue as I had ever seen it," said Schwartz, 60.
Longtime friends and colleagues, Schwartz and Vinci were both assigned to the Secret Service field office at the World Trade Center in 1999.
On that September morning, Schwartz said he was supervising four new interns. He had gone up to the office to grab a few things before meeting them for their first day on the job when he heard the sound of the first plane crash. Schwartz said he quickly guided a group of administrative staff to the ground floor.
Meanwhile, Vinci had spent the morning in the building’s gym and was preparing to attend a meeting about the upcoming United Nation General Assembly, a high-security event that brings together more than 150 heads of state every fall.
After hearing the initial blast and feeling the building shake, however, Vinci grabbed an emergency medical kit and ran down to the plaza to help the injured.
"I saw things that people should never see," said Vinci, who still finds it difficult to watch any news coverage of the attacks. "This is probably the most I’ve spoken about it to anyone."
Vinci spoke to ABC News on the condition that his picture not be published in this story.
Both men spent the rest of the day guiding people out of the area, helping New York City Police Department officers get people onto ferries, and assisting with recovery efforts.
By the end of the day, the building where their offices were based -- 7 World Trade Center -- had also collapsed.
But both Schwartz and Vinci returned to work the following morning. What they found was both a job, and a place forever changed.
Seventeen years later, both men still wake up and head to the World Trade Center every morning. Now retired from their careers as Secret Service agents, they are still tasked with keeping the complex safe as its private security directors.
Vinci started first, in 2016, and is now in charge of two of the six towers in the 16-acre complex on the west side of lower Manhattan.
Schwartz joined him the following year as the head of security at 7 World Trade Center, the building that replaced the one he worked in as a Secret Service agent.
Every day, Vinci and Schwartz walk past the site of the 9/11 Memorial, with its cascading waterfalls that spill into two reflecting pools, contained by panels inscribed with the names of every person who was killed in the terror attacks that day.
Although both men said that they still avoid watching news reports that trigger memories of the attacks, they said they never hesitated to accept jobs at the new World Trade Center.
"It’s nice to be part of this, coming back to what it should have been," said Vinci. "I’m certainly nobody special. I tried to help -- coming back is a continuation of trying to help people know that it didn’t stop because of ."
"The brave people, their names are over there," he added, gesturing to the names of first responders etched into the memorial.