The father of a 17-year-old girl who was stabbed to death in a park has said his “kind” daughter “didn’t deserve” to be killed.
Jodie Chesney was knifed in the back while playing music with friends in the east London park on Friday.
Police now believe “up to four” attackers were involved, having previously been searching for two men.
Jodie’s father Peter said: “Someone knows who did this. Jodie needs justice.”
A 20-year-old man arrested in Leicester on Tuesday on suspicion of Jodie’s murder remains in custody. A magistrate earlier granted police an extension to the custody time limit.
At Scotland Yard on Thursday, Mr Chesney said whoever had killed his daughter was “horrendous”, and urged anyone with information about the attack to come forward.
“Someone knows who it is,” he said. “You can’t get kudos for stabbing a 17-year-old in the back.
“So, just dob them in, grass them up, this is not all right.”
Mr Chesney said his daughter had lost “so much blood” in the “ferocious attack” and that clearly “someone meant to murder her”.
Jodie was with friends near a children’s playground in Harold Hill when she was stabbed in a seemingly motiveless attack.
She was pronounced dead just over an hour after officers were called to the park in Romford, east London, at about 21:25 GMT.
Asked what Jodie was like, Mr Chesney said she was a “proud geek” and a “great girl”.
He said the fibre of her being was “just about being good and kind. There was nothing bad in her body”.
Mr Chesney said Jodie’s death had torn the family apart and that they were “a mess”, adding: “We don’t know how to deal with it.
“Everyone is suffering because she was so good. Everyone just can’t believe – why her?
“It is not that one life deserves to be killed over another, but specifically her, she was so kind.”
Jodie’s stepmother Joanne said the teenager was “very dry” and “did not have a filter” – always speaking her mind whether someone wanted to hear it or not.
Mr Chesney was wearing a purple ribbon made by Jodie’s friends.
He said her peers were dyeing their hair purple in her honour as it was her favourite colour.
Jodie was the fifth teenager to be stabbed to death in the capital so far this year.
Det Ch Insp Dave Whellams, who has been an officer for more than 30 years, said Jodie’s killing was “one of the worst I have come across” because it was “completely motiveless”.
He added: “I think day by day as the investigation progresses we get closer and closer to the truth, and closer to identifying who they are.
“I believe there’s more than two of them involved, possibly up to four, and that one of them is black and one of them is white.”
Det Ch Insp Whellams also said he could not remember a spell of knife crime so bad during his time in the force.