Det Ch Supt Jon Groenen said: “This is a tragic incident and our thoughts are with the child’s family, as well as all those who knew her.
“Our teams are working hard to build a picture of what happened and a significant police presence will remain in Pyrcroft Road over the coming days.
“We appreciate that the incident itself, as well as the significant police presence, will be concerning for residents and we would like to thank them for their cooperation as we conduct our investigation.”
The force said: “At this stage, we are not looking for anyone else in connection with the incident.”
On Friday, bouquets of flowers were left at the entrance to Syward Place, a flat complex on the corner of Pyrcroft Road and Bell Bridge Road. One resident said of the incident: “It’s tragic. Things like that don’t happen around here.”