It would be up to the police to rule these people out, they haven't come forward have they?
Lets see, if say April Jones little friend hadn't seen April get into that car, and a witness said she saw a man standing about where April went missing, are you saying that this man who was seen shouldn't be found and ruled out?
Or it is just the Madeleine McCann case where these things are not supposed to happen?
Precisely, Lace.
In the scenario to which you refer, the man should have been traced to determine if he was the perpetrator or not, and to determine if he had seen anything which might have been useful in tracking down the perpetrator.
The fact that witnesses came forward to say they had seen a man, does not mean he was connected to the crime, but that has to be determined by detective work ... and it seems no-one bothered until DCI Redwood did.
The initial investigation floundered on the lead detective's theory ... the fact that all avenues of investigation hadn't been followed through in preference of that is indicative to me of his unsuitability for the task of searching for a missing child.