Oscar Pistorius says he mistook Reeva Steenkamp for an intruder and shot her out of fear, while prosecutors say he planned the killing and attacked her as she cowered behind a locked bathroom door

The prosecution case against Oscar Pistorius began to unravel on Wednesday with revelations of a series of police blunders and the lead investigator’s admission that authorities have no evidence challenging the double-amputee Olympian’s claim he killed his girlfriend accidentally.

Detective Hilton Botha’s often confused testimony left prosecutors rubbing their heads in frustration as he misjudged distances and said testosterone banned for professional athletes in some cases was found at the scene, only to be later contradicted by the prosecutor’s office.

The second day of what was supposed to be a mere bail hearing almost resembled a full-blown trial for the 26-year-old runner, with his lawyer, Barry Roux, tearing into Mr. Botha’s testimony step by step during cross examination.

Police, Mr. Botha acknowledged, left a 9 mm slug from the barrage that killed Reeva Steenkamp inside a toilet and lost track of illegal ammunition found inside the house. And the detective himself walked through the crime scene without wearing protective shoe covers, potentially contaminating the area.

Authorities, Mr. Roux asserted, were selectively taking “every piece of evidence to try to extract the most possibly negative connotation and present it to the court.”

The case has riveted South Africa, with journalists and the curious crowding into the brick-walled courtroom where Mr. Pistorius, dubbed the Blade Runner for his prosthetic legs, faces a charge of premeditated murder in the Valentine’s Day slaying.

Mr. Pistorius says he mistook Steenkamp for an intruder and shot her out of fear, while prosecutors say he planned the killing and attacked her as she cowered behind a locked bathroom door.

The day seemed to start out well for the prosecution, with Mr. Botha offering new details of the shooting that appeared to call into question Mr. Pistorius’ account of the moments leading up to the 29-year-old model’s death.

Ballistic evidence, he said, showed the bullets that killed her had been fired from a height, supporting the prosecution’s assertion that Mr. Pistorius was wearing prosthetic legs when he took aim at the bathroom door. The athlete has maintained he was standing only on his stumps, and felt vulnerable and frightened as he opened fire from a low position.

Projecting a diagram of the bedroom and the bathroom, prosecutor Gerrie Nel said it showed Mr. Pistorius had to walk past his bed to get to the bathroom and could not have done so without seeing that Steenkamp was not asleep there.

“There’s no other way of getting there,” Mr. Nel said in disputing Mr. Pistorius’ claim that he had no idea Steenkamp was no longer in bed when he pumped four bullets into the bathroom door, striking her with three.

Mr. Botha backed the prosecutor up, saying the holster for Mr. Pistorius’ 9 mm pistol was found under the left side of the bed, where Steenkamp slept, and it would have been impossible for Mr. Pistorius to get the gun without checking to see if she was there.

“I believe that he knew that Reeva was in the bathroom and he shot four shots through the door,” the detective said.

Mr. Botha described how bullets struck Steenkamp in the head and shattered her right arm and hip, eliciting sobs from Mr. Pistorius, who held his head in hands.

Testimony began with the prosecutor telling the court that before the shooting, a neighbour heard “nonstop” shouting between 2 a.m. and 3 a.m. at Mr. Pistorius’ upscale home in a gated community in the capital, Pretoria.

At one point, Mr. Botha told the court that police found syringes and two boxes of testosterone in Mr. Pistorius’ bedroom testimony the prosecution later withdrew, saying it was too early to identify the substance, which was still being tested.

“It is not certain (what it is) until the forensics” are completed, Medupe Simasiku, a spokesman for South Africa’s National Prosecution Agency, told The Associated Press. It’s not clear if it was “a legal or an illegal medication for now.”

The defence also disputed the claim. “It is an herbal remedy,” Mr. Roux said. “It is not ... a banned substance.”

Still, Mr. Botha offered potentially damaging details about Mr. Pistorius’ past, saying the athlete was once involved in an accidental shooting at a restaurant in Johannesburg and asked someone else “to take the rap.”

The runner also threatened men on two separate occasions, Mr. Botha said, allegedly telling one he’d “break his legs.”

The detective said police found two iPhones in Mr. Pistorius’ bathroom and two BlackBerrys in his bedroom, and none had been used to phone for help. Guards at the gated community did call the athlete, Mr. Botha said, and all he said was- “I’m all right,” as he wept uncontrollably.

Mr. Roux later suggested that a fifth phone, not collected by the police, was used by Mr. Pistorius to call for help.

The question now is whether Mr. Botha’s troubled testimony will be enough to convince Chief Magistrate Desmond Nair to keep Mr. Pistorius in prison until trial. While Mr. Pistorius faces the harshest bail requirements under South African law, the magistrate has said he would consider loosening them based on testimony in the hearing. Final arguments were scheduled for Thursday.

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