An unidentified man poured a flammable liquid over his head and set himself on fire on the steps of the U.S. Capitol yesterday, and burned to death as onlookers watched.

It was not immediately clear who the man was or why he did it, said U.S. Capitol Police spokesman Dan Nichols. Investigators were able to determine only that the self-immolated body was that of a white man.

The incident began just before 2 p.m. on the Lower West Terrace of the U.S. Capitol, overlooking the Mall. The fire burned for only a few minutes.

Larry Schuster, a writer for medical publications, said he was about 100 yards away when he heard a sound similar to the burst of flames in lighting an outdoor grill. "The flames were so all-encompassing that you couldn't tell what the object was," he said.

"At first I thought it was a flag-burning demonstration, but as it {the fire} died down I slowly started to see the shape of an arm," Schuster said. "Then I thought it was an effigy. In no way did I think it was a human being."

Nichols said Capitol Police put out the flames with a portable fire extinguisher. Investigators found evidence of an accelerant, which caused the flames to quickly burn the body beyond recognition.

Shortly after the fire was put out, units of the D.C. Fire Department arrived. The man was pronounced dead at 2:07 p.m.

Nichols said Capitol Police cordoned off the area, and with the badly charred body still on the steps, searched the area with dogs to find out whether the man had left another device to start a fire. Nothing was found.

Because the incident involved a death, members of the D.C. police's homicide branch were called to investigate.

Congress is not in session, and Nichols said there were relatively few people in the area when the self-immolation began.

After the body was taken to the D.C. Medical Examiner's Office, officials found a Toyota key in the victim's pocket, Nichols said. Capitol Police searched the area and found a white pickup truck in the 100 block of Pennsylvania Avenue NW, in which the key fit. After another search by bomb-sniffing dogs, police entered the truck and recovered physical evidence, which Nichols declined to identify.

The truck did not have tags, but police were seeking the name of the owner through the vehicle identification number, Nichols said.

The last time that a public self-immolation occurred in Washington was in 1986, when a 58-year-old unemployed insurance underwriter burned himself to death in front of the White House. Police later found a letter to President Reagan inside the man's car.

The last suicide attempt at the Capitol occurred in August 1989, when a man in a wheelchair plunged a knife into his abdomen, shortly after handing police a letter to President Bush. He survived.

Schuster said that immediately after yesterday's fire was put out, investigators gathered witnesses for interviews. At that time, Schuster said, an unidentified woman told him that she watched the man pour a clear liquid on his head shortly before she saw the flames.

The woman, who was being interviewed by police and could not be located, told Schuster that she had been on the lower level of the terrace a few minutes earlier and did not see the man.

Schuster said that despite the intense flames, he never heard a sound or scream from the man.

The supine body was burned beyond recognition from the front side, its legs curled inward.

D.C. police are asking for help in identifying the man. They described him as being in his forties, with graying hair. He wore matching bracelets and a University of California at Santa Barbara T-shirt over a white turtleneck. He had a zip-up jacket and gray pants over dark blue jogging pants. Anyone with information is asked to call 202-727-4347.