But early on Thursday morning, the police arrived at Mr. Pistorius’s house in a gated community in Pretoria to find Ms. Steenkamp, 30, dead from multiple gunshot wounds in a puddle of blood. And before the day was out, Mr. Pistorius, 26, who ran on carbon-fiber blades that earned him the nickname Blade Runner, had been charged with murder.
Early news reports here that Mr. Pistorius, a gun enthusiast, had accidentally shot his girlfriend, thinking she was intruder, gave way to grim police news conferences announcing previous law enforcement complaints about domestic incidents at his home and the current charges of murder. The development stunned a nation that had elevated Mr. Pistorius to the status of a national sporting hero, an emblem of the ability to overcome acute adversity and a symbol of South Africa’s ability to project achievements onto the world stage.
“He was an icon for South Africa,” said Hennie Kotze, one of the coaches who worked with Mr. Pistorius as part of the 400-meter relay at the London Olympics. “It was the way he handled his disability with such character and discipline. It is a big shock for everyone.”
Mr. Pistorius was arrested on Thursday and taken to a Pretoria jail, where he will spend the night in anticipation of a bail hearing to be held Friday morning. The police have said that they plan to oppose bail in the case.
Mr. Pistorius, 26, won two gold medals and a silver at last year’s Paralympic Games in London. In the 2012 Olympics, he reached the 400-meter semifinal and competed in the 4x400 meter relay.
In the Paralympics last September, Mr. Pistorius won individual gold, when he successfully defended his Paralympic 400-meter title. He had lost his 100- and 200-meter titles, but was part of the gold medal-winning 4x100 meter relay team. He came in second in the 200 meter race.
After that contest, Mr. Pistorius damaged his reputation among his followers by criticizing the winner, Alan Oliveira of Brazil, raising questions about the length of the winner’s blades. Mr. Pistorius later apologized and praised the gold medalist in the 100 meter race, Jonnie Peacock of Britain.
Mr. Pistorius, who was born without fibulas, had both legs amputated below the knee before his first birthday, and he battled for many years to compete against able-bodied athletes. In 2008, he qualified for the Beijing Games but was ruled ineligible by track’s world governing body because his blades were deemed to give him a competitive advantage.
“The best case is that he shot her by mistake,” said Hagen Engler, a journalist who edited FHM, a magazine that frequently featured Ms. Steenkamp, whom he knew well. “And that is a particularly South African mistake, that we are so paranoid you are ready to fire off bullets when you don’t know is coming. We are such a messed up country in some ways, and every now and then it comes to the surface with events that bring it into such stark relief.”
Henke Pistorius, Oscar’s father, said in a telephone interview: “I wasn’t there; I have too much respect for Oscar to speculate. I have no clue what happened. The only person who can make any statement will be Oscar himself.”
Asked if his son’s relationship with Ms. Steenkamp had been troubled, Mr. Pistorius said, “Not as far as I know. But I don’t discuss my son’s relationships. I have in fact not met the lady. I don’t know.”
He said that his son had “been in an excellent frame of mind” and had been training for the upcoming track season.
In a nation where violent crime is an everyday fact of life and the culture of gun ownership is well entrenched, many people have handguns at home for self-defense. In an interview with a writer for The New York Times Magazine published in 2012, Mr. Pistorius said he had a 9-mm pistol and had wielded it in response to a false burglar alarm at his home. When asked how often he went to a shooting range to practice, Mr. Pistorius answered, “Just sometimes when I can’t sleep.”
On Twitter, Mr. Pistorius posted recently about another false alarm that may have prompted him to grab his weapon.
“Nothing like getting home to hear the washing machine on and thinking its an intruder to go into full combat recon mode into the pantry!” he posted on Nov. 27.
Adele Kirsten of Gun-Free South Africa, an anti-gun violence organization, said that whatever the motive, the shooting was an avoidable tragedy.
“The idea that you have a gun to protect your family against intruders, the data doesn’t bear that out,” Ms. Kirsten said. “What it tells us is that having a gun in your home puts you and your family at risk of being shot.”
Homicides involving guns have declined in the past decade, Ms. Kirsten said, a development many here attribute South Africa’s Firearms Control Act, which became law in 2004. It restricts South Africans to one gun for self-defense purposes, either a handgun or shotgun. Exceptions exist for regular hunters, but all weapons must be licensed, and gun owners were required to demonstrate that they were trained in gun safety and were free from mental instability and substance abuse.
