JOHANNESBURG (AFP) - Police suspected the brother of Oscar Pistorius of wiping data from the Olympian's phone in the days after he killed his girlfriend Reeva Steenkamp, a South African radio station claimed on Thursday.

Investigators believed Carl Pistorius synchronised his computer with his brother's iPhone, wiping out the entire call history and all WhatsApp messages, according to an investigation by Eyewitness News (EWN).

Police "considered charging him with defeating the ends of justice but ultimately declined to proceed with a case against him", EWN said.

It also revealed that Oscar Pistorius spoke to an ex-girlfriend, Jenna Edkins, just minutes before he came home to Steenkamp on the fateful night of Feb 14, 2013.

Edkins, who dated the runner on and off for several years, was stored in his phone under the pseudonym "Babyshoes".

The call was never raised during the trial, but EWN reported that both the prosecution and Pistorius's lawyers knew about it, and that Edkins was prepared to testify in the runner's defence if the phone call was used.

Pistorius is due back in court on Oct 13 to be sentenced after the judge ruled last month he was guilty of culpable homicide, but not murder.

The new revelations are included in a book on the trial by two EWN reporters released on Thursday.

It says police sought assistance from Apple in the United States to gather information on Carl Pistorius's actions.

In a statement, the Pistorius family reacted in advance to the EWN article.

"We are not sure of the allegations which are to be made or the source of such allegations, but we are not aware of any deletions having been affected by Oscar or effected on his instructions that could be relevant to this trial or could have impacted on this trial," the statement said.

Pistorius, a 29-year-old double amputee, admitted firing through a locked toilet door and killing is model girlfriend on Valentine's Day 2013.

He said he thought he was shooting at an intruder and that Steenkamp was safely in bed.