The husband of Special Constable Nisha Patel-Nasri has been arrested over her murder, sources said today.
Fadi Nasri, 33, was held on suspicion of murder at an address in north London.
Mr Nasri, who runs a limousine business, is at a west London police station. He is the fourth man to be arrested over his wife’s murder.
Scotland Yard said: "A fourth man has been arrested this morning in connection with the murder of Special Constable Nisha Patel-Nasri.
"The 33-year-old man was arrested at an address in north London and is currently in custody at a west London police station."
Another man, who is 37 and was arrested last year, is also being interviewed again today in connection with the case.
Two men have already been charged with the murder of Mrs Patel-Nasri in Wembley, north west London, in May last year.
The two men already charged with Mrs Patel-Nasri’s murder are Tony Emmanuel, 41, of Clements Road, East Ham, east London, and Jason Jones, 35, of Hathaway Crescent, east London. They are next due at the Old Bailey on March 16.
Mrs Patel-Nasri, 29, died after being stabbed in the leg by an attacker outside her home in Sudbury Avenue, Wembley, north west London, on May 11.
It is still unclear whether she had gone outside in her nightdress that night to investigate a disturbance, or whether she found someone in her house.
The motive for the attack on Mrs Patel-Nasri has always been unclear.
She was killed with a distinctive 11.8in (30cm) John Lewis Evolution cook’s knife which was missing from a block set in her kitchen after the attack.
It was later recovered by police and found to carry not only Mrs Patel-Nasri’s DNA, but also that of her suspected attacker.
Mrs Patel-Nasri had been a special constable for three and a half years.
She and her husband had been celebrating their wedding anniversary on the night of the attack. He left the house shortly before the murder.
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.
In September, police appealed for information about an Audi A4 car, which was seen close to Mrs Patel-Nasri’s home - on a possible escape route - just before and after the stabbing.
At the time, police said it could have been directly involved in the crime.
It was seen in Harrowdene Road, which runs parallel to Sudbury Avenue, on two occasions on the night of Mrs Patel-Nasri’s death.
It was later discovered on November 30, but at the time police refused to disclose where except for saying at a "street in south west London".