Vital clues in the hunt for a station knifeman have been denied to police because the CCTV system was faulty.
Wood Street Station is still closed
The victim staggered down the stairs of Wood Street train station in Walthamstow, east London, after being attacked at about midnight on Monday.
Officers are still unsure of where he was assaulted and have been unable to identify the murder victim.
And although the station is covered by CCTV, a police spokesman said: "It appears it was not operational."
A spokesperson for One Rail, which installs and operates the cameras, said the problem was with the recording equipment.
She added: "We are launching our own internal investigation into why this system was not working at the time of the incident and, with immediate effect, will be reviewing all our procedures for the maintenance of such systems at all our stations."
Detectives described the victim as white and aged in his 50s. He was wearing a grey jacket, grey trousers and white shirt.
Officers believe he may have given the name 'John' to the ambulance crew that was called by passengers at the station.
Detective Chief Inspector Ron Scott said: "We are appealing to anyone who may be missing a loved one to contact us.
"It appears that the victim had been heading home and someone must be anxious for his whereabouts. It is essential that we identify him as soon as possible. "
A post-mortem examination showed the cause of death was loss of blood resulting from a stab wound to the stomach.
Wood Street station remains closed.