JOHANNESBURG — She was a platinum-haired model on the cusp of the big time, about to make her debut on a reality television show. He was a global sports hero who, despite having had both legs amputated at the knee as an infant, ran so fast that in a 2011 Nike advertisement he declared, “I am the bullet in the chamber.” Reeva Steenkamp, the model, and Oscar Pistorius, the Paralympic champion and Olympic competitor, were glamorous young fixtures on the South African celebrity scene.

But early on Thursday morning, the police arrived at Mr. Pistorius’s house in a gated community in Pretoria to find Ms. Steenkamp in a puddle of blood, dead from gunshot wounds. 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 an intruder, gave way to grim police news conferences announcing previous law enforcement complaints about domestic episodes at his home and the charge of murder. The development stunned a nation that had elevated Mr. Pistorius as an emblem of the ability to overcome acute adversity and a symbol of South Africa’s ability to achieve on the world stage.

“He was an icon for South Africa,” said Hennie Kotze, one of the coaches who worked with Mr. Pistorius on the 4x100-meter relay at last summer’s London Olympics. “It was the way he handled his disability with such character and discipline. It is a big shock for everyone.”