Police hope that Alex, who was found clinging to his mother's bloodstained body, will provide clues to the killer's identity.
The officer leading the investigation, Detective Superintendent John Bassett, admitted yesterday that the police had no new leads and were pinning their hopes on information from the boy. Ms Nickell, 23, was raped and stabbed to death as she and Alex walked with their dog on the London common. Alex is being interviewed by a team which includes psychiatric experts and a woman officer from Scotland Yard's child-protection team.
Det Supt Bassett said: 'He is talking and it's very encouraging. It would be marvellous if he could turn round to me and give a brilliant description and photofit - of course I'm hopeful.'
Alex appeared to have been traumatised by what he witnessed and did not speak for a long time after the attack. He is now at home with his father, Andre Hanscombe, 29, who said his son was showing incredible strength.
'He's literally carried on as though it didn't happen.'