The husband of special constable Nisha Patel-Nasri has been arrested in connection with her murder.
The couple had been married three years
Fadi Nasri was held on Tuesday morning over the fatal stabbing outside their home in Wembley, north-west London, in May 2006.
The 33-year-old, who was detained at an address in Wembley, is being questioned at a west London police station.
Mr Nasri is the fourth person to be arrested over his wife's death. Two men have been charged with her murder.
Jason Jones, 35, of Hathaway Crescent, and 40-year-old Tony Emmanuel of Clements Road, East Ham, both east London, are due at the Old Bailey on 16 March.
Another man, 37, was also being interviewed by police on Tuesday. He was arrested last December and then bailed pending further enquiries.
It is understood Mr Nasri no longer lives at the home he and his wife shared in Sudbury Avenue.
Mrs Patel-Nasri, who worked as a hairdresser, had been a special constable for three and a half years.
She and her husband had been celebrating their third wedding anniversary on 11 May, the night of the attack.
More than 100 police officers formed a guard of honour at her funeral.
Mr Nasri read a eulogy at the service at Golders Green Crematorium in north London.