A man in his 20s was arrested today in connection with the murder of 16-year-old Mary-Ann Leneghan.
Police raided three addresses in south London at 4am and arrested the man, who is being held in custody awaiting questioning.
A £10,000 (almost €15,000) reward has been offered for information into the death of the teenager from Reading in Berkshire.
Her body was found with a stab wound to the neck in Prospect Park, Tilehurst, Reading, early on Saturday.
Her 18-year-old friend remains in a serious but stable condition in hospital after suffering a shotgun wound.