A report into the Damilola Taylor murder inquiry in Britain identifies a series of failings by the police and criminal justice system.
In particular, it criticises the way the Crown's 14-year-old witness, known as Bromley, was dealt with.
The judge threw out her evidence in the trial of four youths accused of murdering the 10-year-old boy. The Old Bailey trial ended in April.
The eight-month review, which acknowledges the Metropolitan Police have moved on since the botched Stephen Lawrence inquiry in 1993, makes 23 recommendations.
It praises the police's response in the initial stages of the investigation, but adds: "The post-charge phase of the investigation and the associated work necessary in preparing the case for trial was less well managed.
"Dealing with the circumstances of the vulnerable child witness Bromley and her evidence presented significant challenges to the investigation.
"In hindsight, Bromley should have been interviewed in better ways. The absence of any process to test the veracity of Bromley's testimony before trial left the prosecution of the case vulnerable to problems.
"The apparent differences between the way courts treat vulnerable young persons who are witnesses rather than victims or defendants requires further attention."
The report also criticises the way police tried to gather information on the four defendants while they were on remand in young offenders' institutions.
The report said: "The strategy of establishing if the defendants had made incriminating remarks whilst in custody was innovative but poorly resourced. The lack of guidelines, skills and training in this difficult area left some of the evidence subsequently obtained unnecessarily vulnerable to challenge."
PA