Javier Soto spent Friday with his camera, following the standard itinerary for tourists in the nation’s capital. While his wife was attending a medical conference, he took pictures of the Smithsonian, the Washington Monument and the Lincoln Memorial. Then he went to see the Thomas Jefferson Memorial and the White House.

Finally, he returned to the National Mall and, just before 4:30 p.m., aimed his camera east, toward the Capitol.

“That was the last stop that I had planned,” he said.

As he was shooting, a man appeared in the center of his frame, standing near Seventh Street, with his back to Soto. He poured gasoline over his body from a canister, and, before igniting the fuel with a lighter, gave the Capitol a crisp military salute.

Soto’s camera kept clicking as flames engulfed the man’s body and passersby rushed to his aid.

“I just kept shooting,” said Soto, 39, of Little Rock. “I didn’t know what to do in that moment.”

The entire sequence of events lasted about a minute, according to his camera’s data. Once Soto realized what had happened, he joined the small group trying to help the man.

They removed their clothing and used it to try to smother the flames. The man, still conscious when emergency personnel arrived, thanked them for the help, according to accounts from the scene.

Their efforts were in vain. A U.S. Park Police helicopter flew the man to MedStar Washington Hospital Center, where he died about 9 p.m. Friday, according to D.C. police.

On Saturday, authorities still did not know who the man was or why he immolated himself. Because of the severity of his burns, medical personnel would have to try to identify him using DNA analysis and dental records, Officer Araz Alali said.

“This case remains active and ongoing,” he said.

The incident came on the heels of two other unsettling events in the area in the past month.

The man lighted himself on fire just a few blocks from where federal agents killed Miriam Carey after a car chase from the White House to the Capitol. And Washington Navy Yard, where Aaron Alexis shot and killed 12 people last month, is just over two miles away.