A bomb squad member searches an area at U.S. Capitol in Washington on Saturday. The Capitol was locked down after shots were fired and a suspicious package was found after a man from Illinois committed suicide. (Jose Luis Magana/AP)

The sightseers were back at the U.S. Capitol on Sunday, roaming in the brilliant sun in the place where a man had ended his young life in a tragic and spectacular fashion just the day before.

Explanations remained elusive Sunday for what may have helped drive the man, identified in police documents as Leo P. Thornton, 22, to commit suicide — and to do so in one of the nation’s iconic places.

A man who answered the phone at the address police listed for Thornton in Lincolnwood, Ill., declined to comment. An incident report from D.C. police recounted that shortly after 1 p.m. Saturday, “witnesses reported that a lone male subject pulled out a gun, then shot himself in the head.”

Thornton had a brown carry-on bag full of clothes and a sign that Capitol Police Chief Kim Dine said touched on “social justice.” A witness said people who saw the sign told him it read “Tax the one percent.”

Whatever political component may seem to have been at play, said Christine Moutier, chief medical officer at the American Foundation for Suicide Prevention and a former psychiatry professor at the University of California at San Diego, suicide is primarily a mental health problem. Research shows that in more than 90 percent of the 40,000 American suicides each year, an active mental health issue is at play, Moutier said.

A police line is seen near the Capitol on April 11, 2015. (Michael Reynolds/European Pressphoto Agency)

“We often look to external cues, which are absolutely important. But we have done that at the expense of identifying the more internal mental health changes that are taking place that are actually amenable to treatment,” Moutier said. “The fact is that millions of Americans believe different political positions, or lose their job, or get bullied, and don’t actually entertain the idea of suicide. There must be some underlying mental health and cognitive risk factors at play.”

What those might be remained unknown Sunday.

On Saturday, the Capitol was locked down as authorities investigated, including examining Thornton’s luggage. Tourists visiting Congress were held inside until authorities ruled out any further danger or links to terrorism, and most areas reopened within about three hours.

Authorities said part of the western side the Capitol was finally cleared by 2 a.m. Sunday, and by midday the rhythms of one of Washington’s high-traffic cherry blossom weekends were largely back.

Tourists and locals stood by a tiered stone fountain near where Thornton died. Families gathered around each other, interlocking arms for perfect photos in front of the soaring Capitol building.

Most didn’t know a suicide happened there at all. Those who did said they wouldn’t be deterred by such an incident.

“I’m not going to worry about it today,” said Karl Sommer, a 55-year-old brain surgeon from West Virginia who photographed himself near the fountain to catch the scaffolding around the Capitol dome.

Anne Marie Stevenson of Fairfax paused on her bike near the fountain. “I just feel sad,” Stevenson said, “but that’s not going to keep me from going to places.”

The lingering sense of sadness evoked difficult memories for some.

In Switzerland nearly 30 years ago, a man jumped off of a bridge — and Nathalie Mikowicz was standing there.

“I’ve carried it my whole life,” said Mikowicz, a 53-year-old housekeeper from Lompoc, Calif., who said her husband told her about the Capitol suicide while they were touring the area. When she read there were witnesses to the shooting, she was heartbroken.

“When someone tries to hurt themselves, you try to do something about it,” Mikowicz said. “When you can’t, or you’re a witness, it makes you feel used.”

“It’s like your memory gets hogged from the action, and you can never really take it out of your mind,” she said.

A U.S. Capitol Police officer said one or two out of the hundreds who stopped by Sunday asked exactly where Saturday’s suicide happened.

“It’s a part of D.C., I guess,” said Robert Leguizamon, 42, who came from Miami for the Cherry Blossom Festival but emerged Saturday from the National Gallery of Art to see a hazardous materials truck and other emergency vehicles. “I don’t expect it at all, but then, you do expect something.”

“These things happen everywhere,” said Jason Albano, 47, also from Miami.

“But at the Capitol Building?” Leguizamon asked.

Matt Zapotosky and Jennifer Jenkins contributed to this report.