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Her body was found on a path at Linear Park in Culcheth on 11 February by members of the public before she was pronounced dead at the scene.
Police stated that Brianna suffered multiple stab wounds and a post-mortem examination is currently taking place to establish the exact cause of death.
Brianna, from Birchwood, was trans and had been living as a girl for several months.
Cheshire Police initially said there was no evidence to suggest the killing was “hate related” but have since stated that all lines of inquiry were “being explored” – including hate crime.
“All lines of enquiry are being explored, including whether this was a hate crime,” a spokesperson for the force said on 14 February.
“Please continue to avoid speculation online and be wary of sharing misinformation relating to this case.”
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The boy and girl, both 15-years-old, who were arrested on suspicion of murder remain in custody after police were granted a 30-hour extension to continue questioning them.
Brianna’s family described her as a “larger-than-life character who would leave a lasting impression on all that met her”.
“The loss of her young life has left a massive hole in our family, and we know that the teachers and her friends who were involved in her life will feel the same,” they continued.
“We would like to thank everyone for their kind words and support during this extremely difficult time.”
Those who may have information related to the case are advised to contact police via the Cheshire Constabulary website or by calling 101 and quoting IML 1476832. If you wish to remain anonymous, please contact Crimestoppers on 0800 555 111.