The man has appeared via video from overseas at a special night hearing of Mr Edwards’ trial to give his account of the affair.
Prosecutors allege it was the affair this man had with Mr Edwards’ first wife, impregnating her, that was the catalyst to kill.
The man told the court he would always see Mr Edwards on his computer.
“Every night, seven nights a week,” he said.
“He’d come home from work, get changed, go on the computer, come out for a meal, and then go back in again.
“The only time he wasn’t on it was when we were out … throwing ball for softball.
Mr Edwards’ first wife testified last week that his preoccupation with the computer helped end their marriage.
The man, whose identity is suppressed along with those of Mr Edwards two former wives, had an affair with Mr Edwards’ wife while he was a lodger in Mr Edwards’ marital home.
Bradley Edwards has pleaded not guilty to the murders of 18-year-old secretary, Sarah Spiers, childcare worker Jane Rimmer, 23 and Ciara Glennon, a lawyer, 27, between 1996 and 1997.
The 50-year-old Telstra technician and amateur sports official is being tried in a judge-only trial before Western Australian Supreme Court judge, Justice Stephen Bennett.
Earlier on Monday, Mr Edwards was seen to be writing notes as a former Telstra colleague gave evidence about the uniforms the accused allegedly ordered and wore in the mid-1990s.
Part of the prosecution case alleges that polyester fibres, of a particular dye lot called “Telstra Navy” were found on the Ms Glennon, Ms Rimmer and the 1995 Karrakatta Cemetery rape victim.
Telstra employee of 39 years, Robert Kinnear, was questioned about a uniform order by Mr Edwards in August 1995, for navy trousers, and another for a pair of navy coveralls.
The court heard another receipt showed two pairs of navy shorts plus white shirts had been signed by Mr Edwards in November, 1995.
Mr Kinnear told Crown prosecutor Carmel Barbagallo Telstra changed the colour of its national uniform, from grey to blue, in 1994 or 1995.
In April 1996, just weeks before Jane Rimmer was murdered, Mr Edwards ordered a replacement navy jacket, belt and socks.
Mr Kinnear was also asked about its operations in Wellard, south of Perth, where Jane Rimmer’s body was found in August 1996 and a Telstra-issued knife was also found.
No Telstra work had been completed in the area at the time.
Mr Wellard said mapping of underground cabling infrastructure installed by Telstra at Wellard did not specify when it was done.
The Claremont serial killings trial is in its second week and is expected to continue for between six and nine months.
In the hearing’s first week, relatives of Ms Rimmer, Ms Spiers and Ms Glennon, were in court hearing often distressing or disturbing evidence.
Ms Barbagallo alleges DNA and fibre evidence links Mr Edwards to the murders of Ms Glennon and Ms Rimmer and the Karrakatta rape victim.
Mr Edwards has pleaded guilty to the Karrakatta attack and another in the Perth suburb of Huntingdale 1988, but disputes alleged prosecution facts about the assaults.