Paralympic and Olympic sprinter Oscar Pistorius has been charged with murder after allegedly shooting dead his girlfriend Reeva Steenkamp at his home in South Africa.
Her body was discovered at the athlete's home in the Silver Woods country estate in eastern Pretoria, South African police said.
Pistorius reached the 400m semi-finals at the London 2012 Olympics
Initial reports in the South African media suggested Miss Steenkamp was apparently shot as she woke him, trying to surprise him on Valentine's Day, and was mistaken for an intruder.
But police said the shooting was being treated as a murder investigation and that they were "very surprised" by the reports which they said did not come from them.
Brigadier Denise Beukes confirmed the couple were the only ones present in the house at the time of the shooting, and that there had been previous incidents at the premises including "allegations of a domestic nature".
"There are witnesses and they have been interviewed this morning. We are talking about neighbours and people that heard things earlier in the evening and when the shooting took place," she said.
Pistorius was arrested on Thursday morning following the shooting and taken to hospital for a medical examination.
He was due at Pretoria Magistrate's Court this afternoon on a murder charge, but prosecutors said his appearance had been delayed until Friday morning to give forensic officers time to carry out their work.
The 26-year-old is alleged to have shot his 30-year-old model girlfriend in the head and upper body.
Paramedics were called to his home between 4am and 5am local time.
Police arrived shortly afterwards and a 9mm pistol was recovered from the scene.
The shooting took place at Pistorius' home at Silver Woods country estate
They said they would be opposing bail when the suspect appears in court.
"The deceased was shot four times and died on the scene. It is believed that she was the girlfriend of the accused," said police spokeswoman Lieutenant Colonel Katlego Mogale.
Miss Steenkamp's body was removed by a hearse at around 8am.
Pistorius - the world's most famous paralympian - and Miss Steenkamp are believed to have started dating in November.
His father, Henke Pistorius, said of his son: "He is a bit emotional, but he is fine."
There had been speculation the shooting may have been a Valentine's Day surprise gone wrong.
South African journalist Kalay Maistry told Sky News: "It is alleged that he thought his girlfriend, who'd come in to try to surprise him for Valentines Day, was an intruder. It's alleged that he shot her at least twice in the arm and head.
Miss Steenkamp has been described as a "talented and bright young girl"
"I think what this actually highlights is the level of fear ordinary South Africans have.
"This is a man who has gone to bed, it's an innocent surprise from a girlfriend … and the moment he thinks someone is trying to break in he grabs his gun.
"This has come as a complete surprise for a man who's considered a national hero," she added.
Miss Steenkamp, a top South African model and a law graduate from Port Elizabeth, was active on Twitter just 14 hours before.
She tweeted: "What do you have up your sleeve for your love tomorrow??? #getexcited #ValentinesDay"
In response to someone else's plans, she said: "That sounds amazing! Wow that's what it's all about! It should be a day of love for everyone :) may it be blessed!"
Her publicist Sarit Tomlinson said the family was "shocked" and "devastated" by the news.
She described Miss Steenkamp as "the sweetest human being" and "a talented and bright young girl", adding that the couple had a "healthy, fabulous relationship".
Police are investigating the shooting and have launched a murder probe
Photos of the model appeared in newspapers at the weekend, when she described Pistorius as an impeccable man who always had her best interests at heart.
The Johannesburg-born athlete, known as the "Blade Runner", made history in 2012 when he became the first amputee to compete in the Olympics.
He won gold in the 400m and another in the 4x400m relay at the Paralympic Games.
The athlete had both legs amputated below the knee when he was 11 months old, because of a congenital condition, and runs on carbon fibre blades.
Last year Time Magazine named him as one of the world's 100 most influential people.
His London-based agent, Kate Silvers, said she would not be commenting at this stage, but would be issuing a statement later.
Silver Woods, situated in the country's capital, is a high security gated complex with a 3 metre high wall, electric fence, a guarded entrance and regular patrols.
South Africa has some of the world's highest rates of violent crime with an average of nearly 50 people murdered each day.
Pistorius lives in a gated complex in the South African capital Pretoria
Some home-owners carry weapons to defend themselves against intruders. According to statistics, nearly 13 in every 100 people in the country own a gun, and it is estimated there are almost six million civilian firearms.
Pistorius, like many fellow South Africans, appeared to have serious concerns about his safety, and reportedly kept a revolver at his bedside and a machine gun by his window, as well as a cricket bat and baseball bat behind his bedroom door.
South Africa's M-Net cable TV channel said it was pulling an advertising campaign featuring Pistorius off air with immediate effect.
Runner's World magazine editor Mike Finch, speaking from South Africa, told Sky News: "If anybody can overcome this sort of thing it's probably Oscar.
"He's had to deal with a lot in his life. He had a mother that died when he was very young, he obviously has his disability, but yet he's been amazing from a South African perspective as an ambassador.
"There is a certain school of people that don't particularly like him, but I think today everybody has kind of rallied round him."
Both South Africa's Sports Confederation and Olympic Committee and the International Paralympic Committee said they were in no position to comment, but offered their "deepest sympathy and condolences" to the families of all involved.
UN figures show that in South Africa, just over 17 people are killed by gun crime per 100,000 people.
The highest gun death rate in the world is in Honduras with 68 deaths per 100,000. In the USA, the figure stands at 2.97 deaths, while in the UK it is 0.1.