Even allowing for the case being ongoing - it's how many years now? 12?
So far they've not been able to build a case sufficient to charge the 2 people they named as suspects.
DNA testing has advanced in the 12 years, still nothing to support the theory .
That they can't prove an abduction took place does not implicate the McCanns, it just means that they can't say for certain what happened and I would imagine it's harder to disprove an abduction theory than it is to disprove the murder theory.
The fact that they still haven't been able to prove a murder theory speaks volumes.