The family of a schoolgirl stabbed to death in south London had complained of her being attacked before, police said.
The body of Arsema Dawit, 15, was found in a lift at Matheson Lang House, Baylis Road, Waterloo, on Monday.
A post-mortem examination showed that the south London teenager died from multiple stab wounds.
Neighbours and friends said Arsema was being "harassed" by a man and her family had contacted police about it. A 21-year-old man has been arrested.
Police said an allegation of assault and threats to kill against Arsema were reported in April. They added that she had known the man held for her killing.
The man was arrested nearby on Monday and is being questioned by detectives over the killing.
Arsema, who had turned 15 on Friday, is believed to have returned home to the block of flats where she lived when she was attacked.
'Threatened to kill'
Paramedics arrived at the scene within four minutes but were unable to revive the teenager, who suffered multiple wounds, a London Ambulance Service spokesman said.
Det Ch Insp 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."
A Metropolitan Police statement said an allegation of assault and threats to kill against Arsema were made on 16 April in a McDonald's restaurant.
BBC NEWS | England | London | Stabbed girl 'had been harassed'
Stabbed girl 'had been harassed' 
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