On September 11, 2001, Chen Xueli, then a New York City Police Department officer, rushed back to the precinct to change into his uniform and rushed to the scene with colleagues after learning that planes had crashed into the World Trade Center. At the time, he was in the gym of the American Express building across the street; the impact of the World Trade Center buildings collapsing shattered the glass windows, and he survived thanks to the treadmill's shield. As a former Marine, he and his colleagues assisted in evacuating the crowds in the chaos, helping more people leave safely.