The cellphone data that an expert used to map Rob Packham's movements and activities around the time of his wife Gill's murder could be interpreted in many ways, the defence indicated in the Western Cape High Court on Monday.
Advocate Craig Webster, who represents Packham, challenged Warrant Officer Reece Harvey on the evidence he gave about Packham's work and "burner" phones. He testified that the devices were in a certain area because of the location of cellphone towers used to pick up signal.
Harvey's evidence followed that of investigating officer, Sergeant Ivan Sonnenberg, who testified last week that cellphone mapping showed Packham was at key locations where the crimes unfolded on February 22, 2018.
Packham has pleaded not guilty to the murder of his wife and a charge of obstruction of justice. Her charred remains were found on February 22 in the boot of her burnt-out car at the Diep River train station after the fire was extinguished.
Webster handed up a map indicating the locations of the Constantia Dale cellphone tower in Walloon Road (close to Packham's home) and a tower on Main Road (closer to the Diep River train station), about two kilometres away.
"I understand there are places where the signals will overlap with each other," Webster said.
Harvey replied: "My understanding is that the cellphone will pick up the closest and strongest tower".
Webster was surprised at this answer and said he would call an expert to testify on this aspect.
"One is talking about quite a dynamic process where your cellphone is searching for signals," said Webster, referring to variables such as signal strength and how busy a tower was.
He said a tower had a coverage area of up to 20km and if a tower was busy, another tower might be assigned.
Webster commented that Harvey's map, showing the predicted coverage of the two towers, was "extremely misleading".
Harvey replied that the coverage referred specifically to phone calls in this case, based on the call identities that were assigned to a specific tower.
The defence put it to Harvey that if Packham's phone picked up signal at the tower close to Main Road, it meant he was within range of that tower but could still be at his home in Riesling Road.
"I cannot rule it out but I also can't agree with you," Harvey replied.
He added that while a phone could "hop around" towers for GPRS data (used for WhatsApp and internet), it would still choose the strongest and closest tower for calls.
Webster said that the point he was trying to make was that a person might be stationary, even if the data showed different towers.
Harvey earlier testified that on the day of Gill's disappearance, Packham's main phone was switched off between 07:45 and 09:53, when he arrived at work in Bellville. Seven calls were forwarded in this time period.
Under cross-examination, he conceded that a call could also be forwarded if signal was weak or someone was busy with another call.
The State closed its case and the defence will present its case on Tuesday.