The sister of 16-year-old Ben Kinsella, who was stabbed to death on a London street, has made a new appeal to help catch his killers.
Speaking at a news conference in Islington, north london, the former Eastenders actress Brooke Kinsella said "Everybody is scared for their lives".
Ben, 16, was stabbed to death in York Way, Holloway, on Sunday.
On Tuesday, hundreds of people marched through the area in protest over the killing.
Ms Kinsella said: "I know it's fear, for your own life and your family's safety, but if you could do just one good thing in your life and just come forward, just to help give Ben a little bit of justice."
The murder prompted Sir Ian Blair, head of the Metropolitan Police, to "rededicate efforts to stop others dying".
Ben is the 17th teenager to be killed in London since the start of the year.
'Dig a bit harder'
The GCSE student died after a fight in a bar spilled out on to the streets.
The detective leading the hunt for the murderers said the teenager was "entirely innocent" and was killed "in a dispute over nothing inside a pub".
Det Ch Insp John MacDonald appealed for parents to question their children more about closely about their involvement.
He said: "There's no doubt in my mind that some of those kids would've said to their parents: 'I was there but I didn't see anything'.
"Quite frankly, I don't necessarily believe that and I think a lot of the kids would've said that to their parents and their parents would've believed it.
Police say it is unclear how Ben became involved in the disturbance
"What I'd like the parents to do is go back to their children and dig a bit harder and actually find out what was seen."
Three young men, two aged 18 and one aged 19, are in custody after being arrested by detectives investigating the murder.
Miss Kinsella said anyone who knew who was involved in her brother's death should do "one good thing with their life" and give them up to police.
She said that if the roles were reversed, her brother would not have hesitated to help another person.
Miss Kinsella said she knew some witnesses feared for their lives, but insisted police could protect them.
She said: "I have been told that Ben's murder will be really difficult to solve unless those witnesses come forward to help.
"Please do not assume others will tell the police what they need to know.
'Make a stand'
"Do not think that, because arrests have been made, the police have solved the case.
"That is not how it is. We really need you to speak to them."
She added: "Recently, there has been a lot of publicity over knife crime, especially involving young people.
"Yesterday, we marched in Islington to show community opposition to it. But we all really need to make a stand and to help the police."
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