The man could not immediately be identified because his burns were so severe. Medical personnel will try to determine who he was using DNA analysis, Alali said.
Authorities did not say what might have motivated him.
He was standing near Seventh Street and Jefferson Drive about 4:30 p.m Friday when he picked up a brightly colored gasoline canister and doused himself, said Katy Scheflen, a furloughed Justice Department worker who was nearby.
“It didn’t look real,” Scheflen said. “It looked like it would happen in a movie. That’s how fast he went up in flames.”
Scheflen said a jogger running by ripped off his shirt and tried to smother the flames. Soon, others in the area did the same thing. The man was then was airlifted to the MedStar center.
The incident happened just blocks from the scene of a car chase that closed the Capitol a day earlier and set Washington on edge.
Meghan Van Heertum, a tourist from Wisconsin, was walking on the Mall when the incident unfolded. “I saw cops fly up from all directions,” she said.
She said she saw one of the officers kick something that was on fire near the man who was lying on the ground at that point. Van Heertum said she saw flames rising a couple of feet off the ground near the man.
She said the air “smelled strongly of burning flesh.”
U.S. Park Police officers found the man engulfed in flames when they arrived, said Maj. Patrick Smith. He said the incident was under investigation.
“I did not see flames on him, but his face and his arms were charred, and the ground nearby was in flames,” said Nicole Didyk of the District, who was jogging on the Mall when she saw the incident.
Didyk said she spoke to one of the men who helped the injured man. After the flames were extinguished, Didyk was told, the man thanked the people who came to his aid.
There appeared to be a red gas can, a yellow tarp and crumpled newspapers near the scene, in the center of the Mall.
Police had cordoned off a large swath around the area, and dozens of police vehicles were nearby. D.C. police spokeswoman Saray Leon said the man was “conscious and breathing” when firefighters responded.
In a testament to the strange and chaotic week it had been in Washington, a group of tourists snapped photographs of themselves in front of the police tape near the scene, with the Capitol looming in the background.
Max Ehrenfreund and Victoria St. Martin contributed to this report.