As Americans everywhere unite to remember those lost during Sept. 11, Ricardo Mulero, the lead designer of the National September 11 Memorial & Museum exhibition, is opening up about creating an important part of American history and remembrance.

Mulero was in Manhattan's Greenwich Village on the infamous day, NBC News reports. As he got off the subway to go to work, the New Yorker noticed a crowd of people staring at something; just seconds earlier, terrorists had flown United Airlines Flight 175 into the World Trade Center's South Tower.

In May of this year, the National September 11 Memorial & Museum exhibition, designed by Mulero and his Thinc Design team, opened. The team collaborated with the museum's team, engineers, and architects, designing the museum's structure and artifacts displays.

"Unlike any other history project that I have worked on, it was something that I had been part of," Mulero explained. "That became kind of interesting."

Mulero is a Puerto Rican designer who has studied architecture and preservation and previously worked on exhibitions for the U.S. Holocaust Memorial Museum and South Africa's Freedom Park. Commemorating Sept. 11 was still a challenge for Mulero, however, as the museum itself is about 125,000 square feet. Even the museum's artifacts are big; they include the steel frames of the World Trade Center and a fire truck that was there that day.

"We analyzed the space and instead of looking at the obstacles, we tried to look at what were the opportunities here," Mulero said.

The location of the museum was also on display.

Mulero said that his design team decided to take an "austere approach" to the exhibition.

"We maintained that because we felt it evoked the absence of something monumental that was no longer there," he explained. "It was almost like designing an exhibition that was invisible in a way because the objects are so powerful in themselves that they evoke devastation and monumentality."

The Puerto Rican designer was also expected to incorporate the tragedies that occurred at the Pentagon in Washington, D.C. and Shanksville, Pennsylvania.

"Everything has a powerful message or significant story," Mulero said. "Everything has a purpose in this museum."

After four years of work, Mulero hopes that the museum will encourage visitors to fight against future acts of violence.

"For future generations, I hope that they can use such an event as a positive message to better the world and use [the museum] as a resource," he said

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