Police investigating the murder of a special constable on her doorstep have traced a couple who saw a suspect running off.
Mrs Patel-Nasri was stabbed outside her home
They have confirmed a hooded man, who was seen running away after Nisha Patel-Nasri was stabbed, was black.
Police also want to trace another man seen walking away who did not look round as Mrs Patel-Nasri screamed.
She was stabbed just before midnight on 11 May outside her home in Wembley, north-west London.
She was in her nightclothes when she was attacked. It is thought she may have been investigating a noise outside her home in Sudbury Avenue.
One of her kitchen knives is missing - a John Lewis "Evolution" cook's knife which police believe she may have been carrying, only for it to be used against her.
Police said the blade was about 20cm long with the words John Lewis embossed on it, and it would have been covered in blood.
They are also looking for a second man who was seen walking towards East Lane but did not look back despite the victim's screams.
Mrs Patel's knife, of the same type as this one, is still missing
That night, Mrs Patel-Nasri had been out for a meal with her husband Fadi, 32, to celebrate their third wedding anniversary.
Mr Nasri then headed to play snooker but was called back after his wife was attacked.
Officers are keeping an open mind about the motive for the killing.
Scotland Yard confirmed Mr Nasri had been threatened earlier in the year in connection with his limousine business.
High value cars were often parked outside their home and there has been speculation that these may have attracted thieves.
Possible links with an attempted burglary at the house on 6 May are also being looked into.