Twenty-five years after 9/11, Greg Semendinger's aerial photos still transport him back to that fateful day.
Semendinger, a detective and helicopter pilot for the New York City police, had been dispatched to the World Trade Center right after the first plane attack that morning in 2001. As his chopper approached, he could see the giant gash where an airliner had sliced through seven floors near the top of the north tower, and black smoke was billowing out.
Semendinger wasn't an official photographer for the NYPD, but he always carried a camera to document his squad's rescues and had one in the chopper that morning as an unthinkable horror unfolded before him.
He grabbed it and started snapping away.
The images he captured over the next 90 minutes were astonishing, among the only aerial photos of the Twin Towers as they burned and then collapsed, one after the other. With his copilot at the controls and hovering above, Semendinger trained his lens as the second tower vaporized in a plunging cascade of debris, and an immense grey cloud mushroomed across Lower Manhattan.