Police were alerted by a member of the public who had found the badly injured victim travelling in his scooter from a passageway that runs between Runneymede Gardens and Welland Gardens at around 4pm.
A 999 call was placed shortly after 4pm, after Mr O’Halloran revealed he had been stabbed repeatedly.
The pensioner collapsed at the scene as police and paramedics were called, and he was pronounced dead at 4.54pm.
Byer, from Southall, west London, was arrested on August 18, and subsequently charged with Mr O’Halloran’s murder.
At the Old Bailey on Friday, Byer, of no fixed address, pleaded not guilty to murder and possession of a large knife.
Judge Mark Lucraft KC, the Recorder of London, set a pre-trial hearing for February 13 next year.
He was remanded in custody until a three-week trial which is due to start on May 2 next year.