On a wet New Year’s Eve, two police officers were called to a café in Wimbledon where a young woman had collapsed in the doorway, barefoot, bleeding and pleading for help.

Banaz Mahmod, 20, told PC Angela Cornes and a colleague that her father had forced her to drink brandy and tried to kill her. That afternoon, her father, Mahmod Mahmod, had driven her to her grandmother’s house, taken her into the living room and ordered her to consume half a bottle of spirits.

She had never before drunk alcohol. She was told to sit on the floor, facing away from her father, who left, and returned wearing a pair of gloves. Miss Mahmod was dizzy and scared. When she tried to leave the room her father, 52, told her to sit down and suggested that she must be feeling sleepy.

When he again left the room, she fled through the back door and shouted for help, smashing two windows at a neighbouring house to try to raise the alarm. No help came so she jumped over a fence and ran – barefoot and bleeding from cuts to both wrists – to the southwest London café.

Miss Mahmod might be alive today had PC Cornes considered the possibility that she was telling the truth. Instead, the experienced officer, trained in dealing with female victims of violence, sized up the frightened girl and believed her to be a lying, manipulative, attention-seeking drunk.

Customers in the café were puzzled by the officers’ attitude. Nurari Merry, a businesswoman who tried to comfort Miss Mahmod, told The Times that they appeared “slightly offhand”. “She was trying to get somebody to take her seriously, but nobody did. A male officer took notes; the female officer was a little bit dismissive of the situation. They asked her a couple of questions but the ambulance crew took care of it and tried to work out what happened. Police acted as though she was drunk or on drugs.”

PC Cornes broke guidelines by failing to accompany Miss Mahmod to hospital, where she became so terrified of leaving the ambulance that a security guard was summoned to protect her. “My father and my uncle are trying to kill me,” she told a nurse.

PC Cornes contacted Miss Mahmod’s father and arranged to meet him at the grandmother’s house. There, she again broke the rules by telling Mahmod of his daughter’s allegations. Her main focus, however, was on the broken windows next door.

The crime report that PC Cornes filed made no mention of any alleged attempt on Miss Mahmod’s life. Instead, it accused her of responsibility for an act of criminal damage.

A few days later, the officer visited Miss Mahmod, who had left hospital and was back at the family’s home in Mitcham, where she thought her mother would protect her. The officer wanted a signed admission that she had smashed the windows. In a witness statement after Miss Mahmod disappeared, PC Cornes described the young woman – whose naked body was, by now, lying in a makeshift grave beneath a pile of bin bags – as “dramatic and calculating”. When she gave evidence for the defence in the subsequent murder trial, PC Cornes agreed that she had not believed Miss Mahmod’s allegations. She thought she was drunk and seeking attention from her boyfriend.

At the Old Bailey, Mahmod and his brother Ari were convicted of murder in June last year and will serve at least 20 and 23 years in jail respectively.

The trial exposed the insidious brutality of the “honour”-obsessed culture that has dominated sections of the Iraqi Kurdish community in South London. Also revealed were lamentable failings in a policing system that was supposed to provide support and protection to victims of such violence.

Miss Mahmod, one of six children, was 10 when her Muslim family fled Saddam Hussein’s regime. They arrived in Britain with rural tribal traditions that the men of the family were determined to maintain.

When Banaz was 17, she was married to an older man, an Iraqi Kurd from the West Midlands. The two-year relationship was violent. In September 2005 Miss Mahmod fled home. At a family function, she met Rahmat Sulemani, a young Iraqi Kurd, and fell in love with him.

Mahmod forbade the relationship but the couple began meeting in secret. On December 2, a cousin saw them kissing outside a Tube station.

When Mahmod found out, he told Ari, 51, a successful businessman and the self-appointed head of the family. Ari decided that his niece must die. The death sentence was passed at a family meeting. Miss Mahmod’s mother, told of the decision, warned her daughter, who went to the police.

It was the first of what would be four encounters with the Metropolitan Police during which Miss Mahmod claimed that her family were planning to kill her. The third was in the café when PC Cornes was, perhaps, unaware that Miss Mahmod had already given officers a list naming the Kurdish men who she believed had been ordered to kill her. After his brother’s failure to restore family “honour”, Ari would not countenance a second error.

On January 23, Miss Mahmod made her final visit to her local police station to tell officers that Mr Sulemani’s life had been threatened by men who tried to drag him into a car.

Further threats had been made against her life, she said, but she rejected the offer of a refuge and returned home. She wanted the police to know about her fears, she said, in case anything bad happened to her.

The next day her parents left early, by arrangement. Three killers came to the house. Miss Mahmod was beaten, raped and strangled. One of the men was recorded secretly, later, as he complained that she had taken two hours to die and that he had kicked and stamped on her neck for half an hour.

From death threats to a collapsed inquiry

December 4, 2005 Banaz Mahmod tells police of uncle’s threats to kill her

December 5 Police visit her home. She says she does not want to pursue the allegations

December 12 She gives police a letter naming her potential killers

December 31 Her father tries to kill her but she flees. PC Angela Cornes attends and files crime report about damage to a window but makes no reference to the murder allegations. Rahmat Sulemani, with whom Miss Mahmod was in love, records her claims on his mobile phone. She returns to his home

January 2, 2006 Miss Mahmod meets her sisters and mother and is persuaded to return home

January 22 A Kurdish gang threatens Mr Sulemani

January 23 He tells police. Miss Mahmod tells police of death threats. She declines a place in a hostel

January 24 Miss Mahmod is murdered. Police call at the family home. Her father says she is out

January 25 Parents tell police they do not want to report her missing

January 27 Full investigation begins

Date unknown PC Cornes signs statement detailing her impression that Miss Mahmod was a drunken, melodramatic attention-seeker

April 28 Miss Mahmod’s body found in a suitcase in Birmingham

June 11, 2007 Her father and an uncle convicted of murder at the Old Bailey. A third man admits murder

June 18 IPCC announces inquiry

April 2, 2008 Six detectives receive written warning and a constable receives words of advice, but PC Cornes and an inspector are told they will face a disciplinary panel

November 17 All disciplinary proceedings dropped because of “insufficient evidence”. PC Cornes and the inspector are told that they will receive words of advice

November 28 IPCC tells The Times no final decision has been taken to drop disciplinary action, but then confirms that case has collapsed

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