But you are forgetting that it was investigated. And the result was that the McCanns were released from their arguido status because there was no evidence against them.
And that it has subsequently been investigated and the Scotland Yard team have stated that neither the McCanns nor their friends are suspects or even persons of interest in the case.
Such forgetfulness on your part is quite alarming.
Deary me, you just aren't grapsing it are you?
The McCann's had not been fully investigated though, had they? The investigation was incomplete because they refused to co-operate right at the very point that the veracity and truthfulness of what they had said they had done that night could be tested by the way of a reconstruction.
Their hiring of Pinochet's extradition lawyers, and the spurious excuses given by their friends, shows they really didn't want to go back to do that reconstruction, to test their statements and actions.
So no evidence was found against them (in the Prosecutor's mind) in the parts of the investigation that was completed, BUT they refused to take part in one area of the reconstruction aimed at testing their statements.
Had they complied with that request to go back for the reconstruction, as a starting point, for keeping Rebelo's investigation going, then you may have a point.
However given the fact that they bailed out of the investigation right at the time it was specifically looking at their truthfulness, then your point is not valid.