Arnav Gupta, 33. (Montgomery County Police)

Arnav Gupta left his split-level home on Cindy Lane in Bethesda at 9:20 Wednesday morning and was soon reported missing to police. Authorities said they were concerned for his “physical and emotional welfare.”

At 12:25 p.m., police said, Gupta was spotted walking across the grassy expanse of the Ellipse, just south of the White House, engulfed in flames. Authorities said the 33-year-old had set himself on fire, and he died at a hospital later that evening.

D.C. police have taken over the death investigation but revealed few details about Gupta’s public self-immolation that several bystanders captured on video and posted on the Internet. The graphic videos show Secret Service officers in cars and on foot rushing to Gupta, who appeared calm even as he walked several paces while on fire before the officers doused him with foam from fire extinguishers.

Police said they found no notes or other items at the scene to help understand a motive. They searched Gupta’s home near the Congressional Country Club but did not comment on what, if anything, they found. A D.C. police spokesman said the motive remains under investigation.

Relatives did not respond to interview requests by phone and email, and no one answered the door at the house where he lived.

“He really couldn’t have been a nicer kid,” said Kevin Boland, a neighbor who had known Gupta since moving onto Cindy Lane seven years ago.

Boland said Gupta had always struck him as smart, although he had not seen much of him over the past year and a half. He had started to wonder whether Gupta had moved out.

The neighbor said that Gupta never expressed any extreme political views and that his death seemed inexplicable. “This is a tragedy,” Boland said.

Police said it was unclear why Gupta came to the area near the White House, a place frequented by tourists, people with grievances and others.

In April, authorities said a man riding a motorized wheelchair set his jacket on fire outside the White House and was involuntarily committed for psychiatric help. In March 2018, a man from Alabama fatally shot himself in the head along the north fence line of the White House.

Dana Hedgpeth contributed to this report.