The family of murdered schoolgirl Arsema Dawit are demanding to know why police failed to protect her from a stalker who threatened to kill her.

The 15-year-old was stabbed up to ten times in a frenzied attack in the lift of the block of flats where she lived with her family in south London.

A 21-year-old man remains in custody following his arrest on a footbridge over the River Thames after threatening to kill himself.

Detective Chief Inspector Caroline Goode said: "At this stage I am trying to establish the true nature of the relationship between Arsema and the man in custody.

"We are speaking to her family and friends to help build a picture of events leading up to the murder and to help piece together the relationship between them.

Weeks ago Arsema's family told police that she had been assaulted by the obsessive man.

But they said officers told them there was nothing they could do about the man who met her at an Eritrean church where she was a member of the choir.

Scotland Yard has confirmed that police received a complaint on April 30 that a man aged 29 or 30 had assaulted Arsema in a McDonald's restaurant in south London on April 16 and made threats to kill her.

An officer spoke to the girl at her school on May 12 but she claimed to have "no knowledge" of the incident.

Police contacted Arsema's mother a week later and the investigation was still ongoing when she was murdered on Monday.

One source close to the inquiry said officers were not aware of a wider campaign of harassment against the schoolgirl.

Arsema was the 16th teenager to be killed in the capital this year and the first female victim and comes days after Scotland Yard Commissioner Sir Ian Blair vowed to do everything in his power to combat knife crime.

Speaking outside the Dawit family home near Waterloo railway station, friend Simon Tesfaghiorgish said the family were angry and in shock.

He said: "I didn't know him but he had been harassing her. The mother told the police a number of times.

"The police said they couldn't take any action. We are going to complain about this. He beat her and threatened to kill her."

Neighbour Wayne Fort, whose partner and nine-year-old daughter found the body, said Arsema had been troubled by a man in the past.

He saw an argument between the man and Arsema's sister in a stairway in which the girl warned the man not to harm her sister again.

"There was a chap who seemed to be infatuated with her," he said. "He seemed to have met her at the church.

"I could see from the efforts of the elders of the family they were trying to get rid of the man."

Mr Fort said his daughter came banging on his front door crying "Daddy, Daddy, quick, come! The girl's in the lift, she's on the floor, there's lots of blood."

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