The investigation into the murder of 10-year-old schoolboy Damilola Taylor was last night moving into its fifth day amid fears that child witnesses were too frightened to come forward.
Specially trained officers have spoken to 11 youngsters and another 28 interviews have been arranged in south east London.
But police hunting the killers are worried that children who may hold vital information feel they are unable to approach police or even tell their parents.
Witnesses who are too scared to speak to detectives have been urged to contact a Crimestoppers hotline.
Mr Digby Carter, director of the Crimestoppers Trust, said: "We won't ask for names or attempt to trace the call, we offer total anonymity.
"If you are too frightened then for heaven's sake don't sit on your hands, ring Crimestoppers."
The appeal came as religious leaders joined forces to urge anyone with information about the murder to contact police.
In a joint statement church leaders including the Rev Nicholas Elder of St George's Parish Church, and Father Paul Hendricks of Our Lady of Sorrows Roman Catholic Church, said they would also be ready to receive information which would be treated in the strictest confidence.
Detectives have now revealed that a woman recalled seeing Damilola walking alone towards an alleyway just four minutes before he was found bleeding to death on a stairwell after being stabbed in Peckham on Monday.
News of the potentially crucial witness came as Damilola's father, Richard, was reunited with his family in London after flying in to Gatwick Airport from Lagos, Nigeria.
And it emerged yesterday that a child who was seen being marched along a road near the murder scene in Peckham in a headlock on Monday afternoon was not the schoolboy.
The investigation appeared to take another turn when police detained three youths who turned up at the spot where Damilola died.
The three boys, aged in their early teens, had been talking to reporters when the police arrived.
A senior police officer said the boys were being detained but not arrested and there was nothing to suggest they were involved.
A bouquet of flowers from one of the people who tried to save Damilola was among tributes laid at the stairwell.
The anonymous card accompanying the flowers read: "Sorry I could not help you in life. But your soul will be with me in my heart forever. You are in heaven now."
It was signed: "Someone who tried to give you your life back."
Detectives spoke to a boy and a girl who were filmed with Damilola on close circuit television going into a library for an after-school computer class.
The two children, who are not suspects, were asked what their friend was saying in the hour before his brutal death.
Police are exploring the possibility that Damilola was followed from the library by his attackers.
Det Supt David Dillnutt disclosed that a female witness spotted the boy walking past her home along Cronin Street in Peckham at about 4.45 p.m.
At 4.49 p.m. a member of the public rang the emergency services to report a boy bleeding to death. Damilola left a 100-yard trail of blood as he tried to flee his attackers.
Police are looking for three black youths who were wearing dark clothing and were seen running away from the murder scene.