Dr Imran Farooq was on his way home from work when he was attacked outside his home in Green Lane, Edgware shortly before 5.30pm on Thursday 16th September 2010.
A post-mortem gave his cause of death as multiple stab wounds and blunt trauma to the head.
A five and a half inch-bladed kitchen knife and a house brick used in the attack were recovered at the scene.
Detectives from the Met Police Counter Terrorism Command remain committed to finding those responsible.
They believe his murder would have required careful planning and would have required help from other people, some of whom may have provided assistance or information unwittingly.
They want to speak to anyone who was asked for information about Dr Farooq and his routine.
More top news
The robbers casually approached their victim on a busy high street before before spraying a noxious substance in his face.
Tencho Hristov ignored warnings and got trapped between barriers at Roydon in Essex.
The 6km bike track will include 130m of the South Circular near Kew Bridge.