WASHINGTON (AP) A man who set himself on fire on the National Mall in the U.S. capital has died of his injuries, which were so severe that authorities will have to use DNA and dental records to identify him, District of Columbia police said Saturday.The man died Friday night at a Washington hospital where he had been airlifted, Officer Araz Alali, a police spokesman, said.The man poured a can of gasoline on himself in the center portion of the mall Friday afternoon. He then set himself on fire, with passing joggers taking off their shirts to help douse the flames. Police had said he was conscious and breathing at the scene, but he was airlifted to MedStar Washington Hospital Center.Police are investigating the man's possible motives.Lt. Pamela Smith of the U.S. Park Police said she was unaware whether he carried signs or had articulated a cause. One witness, Katy Scheflen, said that she saw a tripod set up near the man but that she did not hear him say anything intelligible before he set himself on fire. It was unclear whether the man was filming the incident.The immolation occurred in a city with jangled nerves following a Sept. 16 mass shooting at the Washington Navy Yard and high-speed car chase outside the U.S. Capitol on Thursday. The chase ended with a woman being shot dead by police with a young child in the car.