Nisha Patel-Nasri, 29, a hairdresser and special constable with the Metropolitan Police, was murdered yards from her house in Wembley, north London, just before midnight on Thursday.
Police believe the off-duty special, who was wearing a nightdress, may have gone outside because she heard thieves trying to break into two cars, one a stretch limousine belonging to her and her husband's limousine hire business.
Neighbours heard Mrs Patel-Nasri screaming and dashed outside to find her lying on the pavement, bleeding from a stab wound to the leg. A man in a hooded top was seen fleeing. Detectives are investigating whether there is a link between her murder and an attempted burglary at her home on Saturday night.
Three black men had tried to break into her house and fled when she challenged them in the porch. One theory being investigated is that one of the men returned to the house.
Mrs Patel-Nasri was alone at home on the night of her murder as her husband, Fadi Nasri, who she married three years ago, had gone out for the evening. She was given first aid by one of her neighbours, who also alerted her husband and called the police.
Kamlesh Chudasma, 35, who lives in the same street, said: "I heard one loud, long scream. By the time I heard the second scream I was out of the door and I saw Nisha standing there with her hand on her stomach.
"There was a lot of blood, she got up and walked to her house and I asked her 'Are you all right'. She said 'No, I got stabbed, call the police'.
"Fadi collapsed one or two times when he saw Nisha had been stabbed. He was crying out 'What's going to happen now' while he was being comforted. She was a very bubbly and nice person and would always take an interest in asking how people were."
When officers arrived she was given further first aid and taken to Northwick Park Hospital, where she later died. Yesterday, there still two large patches of blood on the pavement outside her house.
Mrs Patel-Nasri had been a special constable for three years, working from Wembley police station, and had moved into her current address about a year ago.
Detective Superintendent Julian Worker, who is leading the murder inquiry, said the suspect was likely to have been heavily bloodstained. He added: "What we believe happened is that she's come out of her house in her night dress and dealt with something in the street.
"Nisha was a very well known member of the community. This is an absolutely dreadful crime in tragic, tragic, violent circumstances. We are appealing for anyone who saw a person going home clearly stained in blood as there was a lot of blood at the scene. This sort of crime is atrocious."
The officer confirmed that his team would be investigating whether there was any link to the attempted break-in at her home on Saturday.
As well as being a hairdresser, the victim was the director of a limousine rental company called Limo Lounge Limited, with her husband. The firm reported £8,000 profits last year.
The couple owned the stretch limousine and a black Humvee parked outside their house. Both vehicles were taken away by police to be searched.
Police believe the cars could have been the target for thieves and that Mrs Patel-Nasri could have been trying to intervene when she was stabbed.
Ali Sial, 26, an architect, was working at his home in the street when he heard screams. "She must have stumbled down the road and passed out twice before the paramedics arrived. It was difficult to tell, but I think she said 'Where am I' and then she passed out. There have been quite a few cars down the road which have had their windows smashed.''
The Metropolitan Police Commissioner, Sir Ian Blair, said: "It is a tragedy that a young woman who willingly gave up so much of her valuable free time to work as a police officer in her local community should lose her life in this terrible way. Nisha was tremendously popular with her colleagues, who regarded her as a real team player, and her death is a huge loss to the Metropolitan Police Service."
But the police said the neighbourhood was a low crime area, with burglary down by 32 per cent.
Mrs Patel-Nasri's murder is another example of knife crime in Britain. Recent cases include the murders of the financier John Monckton in Chelsea, south-west London, and that of the teacher Robert Symons in Chiswick, west London, who were stabbed to death during burglaries at their homes.
The police's struggle to find volunteers
By Jason Bennetto
Scotland Yard has been struggling to persuade members of the public to sign up as volunteer special constabulary, or "specials", despite a series of recruitment campaigns.
Nationally, the figures for special constables have been rapidly dropping - from a peak of 20,000 in 1996 to about 13,000 now.
In the Metropolitan Police there are about 1,220 specials, a quarter of whom are women, who work alongside the 30,000 full-time officers.
The special constables, whose jobs were created 175 years ago, are expected to work at least four hours a week. They receive free travel and other expenses.
One of their main roles is to boost the visible presence of police on the street and form a link with the local community. Once they have been trained, they have all the powers of a full-time officer and wear a similar uniform.
The fall in the number of people volunteering is thought to be due to a number of reasons, including a decline in the idea of civic duty, as well as a fear of violence. The introduction of community support officers, civilian police staff who have limited powers, has also undermind the role of the specials.Reuse content