A policeman picked up the firearm believed to have been used in the fatal shooting of Oscar Pistorius's girlfriend Reeva Steenkamp without gloves, the High Court in Pretoria heard on Friday.

Former policeman Giliam van Rensburg said that while he and colleagues were collecting evidence on the morning of February 14, 2013, shortly after the shooting, he heard the sound of a gun being cocked behind him.

He saw the ballistics expert had the firearm in his hands, without gloves.

"So I asked him what are you doing?" said Van Rensburg.

The man looked and saw he was not wearing gloves.

"And then he said 'Sorry'," said Van Rensburg.

The man took a cloth out of his pocket, wiped the gun, and made it safe.

Van Rensburg earlier testified how one of Pistorius's eight wristwatches disappeared from his bedroom while evidence was being collected.

Van Rensburg said he cracked down on access to the Silver Woods estate where the paralympian lived and put barriers around the house making people sign in and out for access, and to sign evidence out in bags.

He also had the house sealed.

"I didn't trust anyone at that stage," he said.

Pistorius has pleaded not guilty to premeditated murder, claiming that he believed there was an intruder hiding in a locked toilet cubicle in his home when he fired four shots into it, fatally wounding Steenkamp.

The trial continues.