United Airlines Flight 175  heads into the South Tower of the World Trade Center on Sept. 11, 2001. (CARMEN TAYLOR/ASSOCIATED PRESS)

A jetliner heading straight for the South Tower of the World Trade Center. A single man falling from the North Tower, choosing to jump instead of die from the fire and smoke. Three firefighters raising a flag they’d found in the rubble. And four people in Brooklyn, seemingly relaxing in the sun as the city burned behind them.

The photo of the jetliner, captured by at least 100 cameras, was reprinted again and again in the days that followed the attacks, representing the improbability of the very event that a U.S. plane could crash headlong on a normal, sunny morning into one of the country’s most important buildings.

The single man falling, a photograph taken by Associated Press photographer Richard Drew, is so shocking in part because it reveals that reactions to the attacks went far beyond the normal. The man’s identity remains uncertain, though Vanity Fair Magazine thinks it could be Jonathan Briley, a 43-year-old employee of the Windows on the World restaurant at the World Trade Center who was asthmatic and knew he could not survive the smoke. For what could be the first time in history, the city’s medical examiner’s office classified those who jumped from the buildings as homicides, not suicides.

A man falls from the North Tower of New York's World Trade Center on Sept. 11, 2001. (RICHARD DREW/ASSOCIATED PRESS)

The photo captured by photographer Thomas E. Franklin of the flag found in the rubble and hoisted up by three firefighters, William Eisengrein, George Johnson and Daniel McWilliams, reveals the connectivity of tragic events throughout history. While Franklin’s photo represented the resilience of these firefighters and other emergency workers on this day, it became iconic because of its connection to the historic Iwo Jima photograph, in which six U.S. Marines raised Old Glory during fighting on the Pacific island in World World II.

Brooklyn firefighters George Johnson, left, and Dan McWilliams, center, both of Ladder 157, and Billy Eisengrein, right, of Rescue 2, raise a flag at the World Trade Center in New York after the Sept. 11, 2001, attacks. (THOMAS E. FRANKLIN/ASSOCIATED PRESS)

A photo that’s harder to reconcile shows a group of people relaxing in the sun in Brooklyn as a giant cloud of smoke and dust rises just across the river. The Guardian’s Jonathan Jones writes that the controversial photo shows that “life does not stop dead because a battle or an act of terror is happening nearby.” While photographer Thomas Hoepker was hesitant to share the photo, Jones writes that it is an important one, because it reminds us that even in the moments after an event happens, life is already moving on.

A group of people relaxes during their lunch break along the East River while a huge plume of smoke rises from Lower Manhattan after the attack on the World Trade Center on Sept. 11, 2001. (THOMAS HOEPKER/ MAGNUM PHOTOS)