Olympic and Paralympic star Oscar Pistorius has been arrested on suspicion of murder after his girlfriend was shot dead at his home.
Initial reports suggested that model Reeva Steenkamp, 30, might have been mistaken for a burglar at the property in the Silver Lakes Golf Estate in the South African capital Pretoria.
But police said the shooting was being treated as a murder investigation, adding that there had been previous incidents of a "domestic nature" at the address on an exclusive gated estate. Pistorius, 26, will appear in court on Friday morning.
Brigadier Denise Beukes said there was no sign of forced entry at the house. There had been speculation that the shooting might have been a Valentine's Day surprise gone wrong.
Miss Steenkamp, described in her Twitter biography as a model, cover girl and law graduate, had tweeted about Valentine's Day yesterday: "What do you have up your sleeve for your love tomorrow??? #getexcited #ValentinesDay."
Pistorius's father said his son was "sad" following the shooting. Henke Pistorius told SABC radio news: "I don't know the facts. If anyone makes a statement, it will have to be Oscar. He's sad at the moment."
Gold medal-winner Pistorius is known as the Blade Runner because of the ground-breaking prosthetics he uses for racing. He made history at the London 2012 Olympics when he became the first amputee sprinter to compete in the able-bodied Games, running in the 400m and 4x400m relay.
Miss Steenkamp's publicist Sarit Tomlinson paid tribute to her, describing her as "the sweetest human being and an absolute angel on earth". She added: "She was the kindest, most unbelievable girl." She told Sky News: "It's shocking. No one knows what happened. We're waiting for information. There are people we are waiting to speak to, to validate some of the stories."
Dressed in a grey hooded jacket, tracksuit trousers and trainers, Pistorius walked with head bowed from the Boschkop police station this morning, before he was taken to Pretoria's Mamelodi Day Hospital in a police convoy. A spokesman for the athlete, from the Fast Track agency in London, said he was "assisting the police with their investigations" but no further comment could be made until matters became clearer.
Athletes joined fans in paying tribute to Miss Steenkamp. Jessica Ennis spoke of her shock on Twitter, describing the "the horrendous news" as "an awful tragedy". London 2012 Paralympic 200m champion Richard Whitehead tweeted: "Shocking news this morning regards my buddy Oscar P what a tragedy!!! Unbelievable I'm speechless #oscar."