Luxury wristwatches went missing from athlete's home on day of his arrest for killing his girlfriend, throwing doubts on murder case

A damning portrait of South African police, contaminating evidence and stealing from the citizens they are supposed to protect, was painted at the trial of Oscar Pistorius on Friday, raising doubts over the credibility of the murder case against him.

Two luxury wristwatches worth thousands of pounds went missing from the Paralympic athlete's bedroom on the day that he was arrested for the killing of his girlfriend, according to Pistorius's defence team. A former police colonel admitted in court that one of the watches had been stolen virtually from under his nose.

The boost for the defence came after the court was shown the first photos taken of Pistorius in the immediate aftermath of the shooting. Bare-chested and looking shellshocked, he was standing on blood-stained prosthetic legs and wearing shorts covered in blood. The "blade runner" denies murder, contending that he shot Reeva Steenkamp through a locked toilet door because he thought she was an intruder.

Former police colonel Schoombie van Rensburg, who was among the first on the scene of the incident on Valentine's day 2013, testified that experts examined a blood-spattered box containing eight wristwatches, worth an estimated 50,000-100,000 rand (£2,800-£5,600), and that one went missing even after he warned his officers against theft. "I saw those watches and I said, this is tempting for any person because these are expensive watches," he told the court.

Van Rensburg described his reaction when he was later told a watch was gone. "I said, 'I can't believe it. We were just there. How can this watch be gone?'"

Suddenly his own colleagues were under suspicion. "We body-searched everyone. We searched the whole house. We even searched the vehicles of every expert at the scene."

This proved fruitless and a theft docket was opened, he said. "I was furious." When van Rensburg visited Pistorius, he told him to "remember he's a celebrity" and report anything that went missing.

Defence counsel Barry Roux put it to van Rensburg that an additional watch that had been lying on top of a cabinet was also missing. The former station commander denied knowledge of a second theft.

Van Rensburg, who retired last December, said he later found another investigator mishandling the 9mm pistol that was used to kill Steenkamp and discarded on a blood-soaked bathroom mat. "At that particular moment the ballistics expert was handling the firearm without gloves," van Rensburg told the court.

"I was busy talking on my cellphone when I heard the firearm had been cocked. I stopped talking and said, 'What are you doing?' He said sorry and put the magazine back in the firearm ... So immediately I was very angry."

The ex-colonel said he recognised the toilet door through which Pistorius shot as the "most valuable" piece of evidence and decided to take it away in the biggest body bag available. He conceded: "As we carried this door, the loose panels of this door were shifting and we were afraid it was going to crack the body bag, which was plastic."

Then there was a problem finding a big enough vehicle to transport the door. Van Rensburg said he stored the door in his office at the police station because it was too big to fit in the area normally reserved for evidence from crime scenes.

The second week of the trial ended with the prosecution confessing that the digital camera used to take photos of the scene had labelled them with the wrong date and wrong year, prompting a scornful aside from Pistorius to his uncle.

Under the world's gaze, the trial threatens to become the latest body blow to the reputation of the South African police. This month alone an official inquiry into the 2012 Marikana massacre heard that some mineworkers were shot dead by officers "execution-style" as they surrendered with hands in the air, while police in Cape Town were caught on video kicking and punching a naked Nigerian man. Last year, a South African parliamentary committee heard that 1,448 members of the police have criminal convictions, including for murder, rape and theft.

Earlier, the court saw two dramatic images of a disoriented, shirtless Pistorius wearing blue blood-soaked shorts and with dried blood on his left arm shortly after the killing. Tattooed words and red tape, apparently because of a sporting injury, were visible on his muscular back.

The trial will resume on Monday.