Nottinghamshire Police have confirmed that the attack on an Egyptian student was not hate-related.
Speaking in Mansfield on Monday evening, Chief Superintendent Rob Griffin said: “The investigation is making really good progress.
“We now know that a group of six girls were involved in the incident and we believe that we have identified all six of those girls.”
One girl has been arrested on suspicion of assault occasioning grievous bodily harm and released on conditional bail.
He confirmed officers would be meeting with representatives from both the Egyptian and Italian embassies later this week.
The engineering student, who studied at Nottingham College was attacked on February 20 whilst waiting for a bus on Lower Parliament Street, near intu Victoria Centre.
Mariam remained in a coma for three weeks, and died on Wednesday, March 14 at Nottingham City Hospital.
The post-mortem examination into her death came back as inconclusive and further tests will be carried out in the next few weeks.
Chief Supt Griffin said: “We are working very closely with Mariam’s family, focusing on ensuring they get proper support at this difficult time, in order to get justice for Mariam and her family”.
The 18-year-old and her sister were assaulted in August 2017 in Nottingham, but police are yet to confirm that the attacks are linked.
“In terms of whether or not the incident in August is connected to the one in February, we are open minded and as investigations continue, hopefully that picture will continue to become more and more clear,” he added.