Searches are being carried out by counter-terror police investigating the murder of Pakistani politician Imran Farooq, Scotland Yard said today.
Two residential addresses in north-west London are being examined and so far no arrests have been made.
Dr Farooq was stabbed to death outside his home in Edgware, north London in 2010 when he was ambushed on his way home from work.
He was a prominent member of the Pakistani political party MQM (Muttahida Qaumi Movement), and had been living in exile in the UK for more than a decade when he died.
In the weeks before his death he had been trying to raise his own political profile and had set up a Facebook page.
Police believe he was attacked by up to four men who had been seen near his house in Green Lane, Edgware, at various different times, apparently watching him.
Dr Farooq died from stab wounds and head injuries when he was attacked with knives and a house brick.
In the last three years investigators have interviewed eight people under caution and searched 10 addresses, but no one has ever been charged with the murder.
A £20,000 reward is available for information leading to the prosecution of Dr Farooq's killers.