A sex attacker pleaded guilty to murdering a mother in front of her baby, just days after being released on police bail.

Eight days before he killed 23-year-old Stacey Westbury last August, crack cocaine addict Christopher Braithwaite had been arrested and interviewed by detectives about the indecent assault and false imprisonment of another woman.

"This is a particularly grave sexually motivated murder," said prosecutor Victor Temple at the Old Bailey after Braithwaite pleaded guilty to murder and sexual penetration without consent.

"He carried out a violent sexual assault on a defenceless young woman which in turn involved sexual abuse accompanied by strangulation."

Braithwaite, 22, who knew his victim because they had gone to the same school but was no more than an acquaintance, murdered Westbury at her flat in Fulham, west London.

Her naked body was discovered by a friend and her father slumped across a sofa. She had been repeatedly stabbed with a kitchen knife. Her 10-month-old son was left in a cot and his cries prompted her father and her friend to break into the flat.

Temple said Braithwaite had failed to tell anyone about the baby being left alone and that he had stolen her bike, jewellery and mobile phone to fund his drug habit.

"I feel that part of my soul has been torn away," said Westbury's father Kenneth in an impact statement.

"All this pain I will carry with me for the rest of my life." Westbury's mother Lorraine said her grandson was now terrified of strangers.

The court heard that a week before the murder, Braithwaite, who had a long list of previous convictions including one for wounding, had been arrested on suspicion of a sex attack on another woman.

The judge agreed to leave nine charges relating to attacks on this woman and another to lie on the court file.