The post-mortem examination into the death of an 18-year-old girl who died three weeks after she was assaulted by a group of women was inconclusive.
Egyptian national Mariam Moustafa died on Wednesday after she was attacked in Nottingham on 20 February.
Police said more tests will now take place to establish if there was a link between the assault and her death.
A 17-year-old girl, who was arrested on suspicion of assault occasioning grievous bodily harm, remains on bail.
Nottinghamshire Police said Miss Moustafa was "punched several times" while waiting for a bus outside the Victoria Centre in Parliament Street.
In a statement, the force said she got on a bus but was followed "by the same group of women who were threatening and abusive towards her before they got off".
Footage of the attack has emerged, which the force confirmed showed part of the assault.
Miss Moustafa's family said she was attacked about 20:00 GMT, taken to hospital and then discharged about 02:00 that night. Miss Moustafa was then taken back to hospital later that day and died over three weeks later at Nottingham City Hospital.
Nottingham University Hospital NHS Trust said its "initial review of this tragic case does not indicate any significant untoward incident on the trust's part, however we will fully examine the family's concerns".
Miss Moustafa's sister Mallak, 16, told the BBC that her sister was born with half a heart.
Talking about the attack, she said: "I don't know if they did it because they knew she had a heart condition."
Police said they were keeping an "open mind" about whether the attack on Miss Moustafa, which has sparked outrage in Egypt, was racially motivated.
Egypt's Foreign Minister Sameh Shoukry said that the "painful incident" of Miss Moustafa's death "cannot go unpunished", adding that any officials responsible for medical negligence should also be held to account, according to BBC Monitoring.
In a statement they said: "Nottinghamshire Police is committed to thoroughly investigating the circumstances around Mariam's death and will bring you factual information at the appropriate time."