Brianna, 16, was stabbed 28 times with a hunting knife in her head, chest, back and neck while in Culcheth Linear Park, near Warrington, Cheshire, in February this year. The defendants, a girl, 16, identified only as X, and a boy, 16, identified only as Y, were both aged 15 at the time. Both deny murder.
Neither can be named by court order because of their age.
At the start of their trial the jury of seven men and five women were told they had made plans to kill other children before killing Brianna.
Girl X also liked to watch "dark web" torture videos and had become "obsessed" with Brianna, born a boy but who identified and lived as a girl, Manchester Crown Court heard.
Girl X, wearing a dress and grey cardigan and boy Y, wearing black trousers and shirt with a grey tie, sat in the dock listening as Deanna Heer KC opened the case for the prosecution.
Ms Heer said Brianna's body was discovered by dog walkers Kathryn and Andrew Vize, at about 3pm on February 11 in the park near Warrington.
This story is from the {{IssueName}} edition of {{MagazineName}}.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.
Already a subscriber ? Sign In
This story is from the {{IssueName}} edition of {{MagazineName}}.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.
Already a subscriber? Sign In
Pep quotes Mourinho as he says top four would be big success
Securing a top four finish would be as big a success as anything Pep Guardiola has achieved at Manchester City believes the manager as he looks to reframe his side's ambitions ahead of a defining run of fixtures.
Bevan showing top scrum potential
THERE are constant murmurings in professional sport about x player improving y about his game.
'Worst in the league when we lose ball'
PEP SAYS OPPOSITION TEAMS NO LONGER FEAR HIS STRUGGLING CITY SIDE
Yet more change on the agenda for Raducanu
Emma Raducanu is searching for yet another coach after Nick Cavaday ended their partnership because of health issues.
Sickening to see Musk gesture just before we remember Holocaust
I WAS horrified to see Elon Musk give what looked like a Nazi salute, twice, as he gleefully greeted the crowd at an inaugura- tion rally this week.
Chelsea wait on Palmer fitness news
CHELSEA are waiting on positive news to discover whether Cole Palmer will be fit to face his former club when they travel to Manchester City this weekend.
Google pledges to crack down further on fake online ratings
GOOGLE has made a commitment to bolster its fight against fake reviews in the UK by taking more robust action.
Ex-football star 'kicked wife in head'
FORMER footballer Joey Barton pushed his wife to the floor before kicking her in the head during a drunken row at their family home, a court has heard.
Murray may stick with beaten Novak
ANDY Murray will discuss with Novak Djokovic whether to continue their partnership after a premature end to the Australian Open.
Lewis points out a culture clash
CRICKET England head coach Jon Lewis accepts his side cannot match Australia for athleticism, speed or power, pointing to a \"cultural difference\" between the nations.