Two 15-year-olds remain in custody after being arrested on suspicion of stabbing 16-year-old Brianna Ghey to death in a park.
The victim, from Birchwood in Warrington, Cheshire, was found by members of the public as she lay wounded on a path in Linear Park, Culcheth, at around 3.13pm on Saturday.
Brianna was a transgender girl but police said there is no evidence to suggest her murder was a hate crime.
A boy and a girl from the local area have been arrested on suspicion of her murder.
Emma Mills, headteacher at Brianna’s school Birchwood Community High School, said: “We are shocked and truly devastated to hear of the death of Brianna.
“This is understandably a very difficult and distressing time for many and we will do our utmost to support our pupils and wider school community.”
He said: “A number of inquiries in relation to this incident are under way and we are doing all that we can to establish the exact circumstances of what has happened.
“At this time, there is no evidence to suggest that the circumstances surrounding Brianna’s death are hate-related.
“Patrols have been stepped up in the local area and officers will remain in the Culcheth area to provide reassurance and address any concerns that residents may have.
“I would ask anyone who has any information, no matter how big or small, that they believe could help with our investigation to get in touch.
“We are also keen for people and businesses within the local community to check any CCTV or dashcam footage for anything that may aid our investigation.”
Anyone with information can contact Cheshire police on 101 or online, quoting the reference IML 1476832.
Information can also be reported anonymously via Crimestoppers on 0800 555 111.