James Dunleavy denies murdering 66-year-old Philomena before dismembering her corpse and burying the remains in an Edinburgh beauty spot.
In his closing speech at the High Court in Edinburgh, defence QC Gordon Jackson said Mr Dunleavy, 40, had a very simple response to the Crown case: "I never."
The lawyer admitted that Mr Dunleavy was "prime suspect" but told jurors suspicion was not enough to convict. Mr Jackson recalled how police and forensic scientists had given evidence about their thorough search of the flat in Balgreen Road - where Mrs Dunleavy, from Dublin, was staying with her son when she died last year.
"CSI in spades. They did it to the nth degree," he said.
Earlier, Advocate Depute Alex Prentice QC, prosecuting, said the case against Mr Dunleavy was a circumstantial one in which pieces of evidence came together like strands in a cable.
The trial at the High Court in Edinburgh continues.