Do you mean not as much material was collected in the first instance or that we only have access to a limited amount? I am assuming Dr Lean had more info for her book? I haven't read the book btw.
Why does anyone have to accept the Crown's case because an alternative isn't currently known about?
The authorities had Colin Stagg marked for the murder of Rachel Nickell but we now know it was actually Robert Napper. Why can't a Robert Napper type be responsible here and just slipped under the radar as Napper did?
I agree that it could be an alternative culprit. However, this would need the case to be reopened by the police and that would likely require grounds. Stagg was freed by the judge before the trial started, because of the over zealous pursuit of Stagg and the 'Honey trap'. The true killer confessed 16 years later and had spent time in Broadmoor for a similar offence.
Though all local alternatives have been eliminated there just remains three remote suspects. Stocky man. Loiterer near the school at car with bonnet up. A person of interest who came to the attention of the police during the reconstruction.
I do not believe the volume of data comes anywhere near that of JB because of all the subsequent investigations and appeals.
The number of victims and the complexity of the crime scene also makes for big differences in evidence. Then there was the sheer number of officers involved etc. etc. Need I go on?