Why did McCanns refuse to answer a single question?

Because they were scared of getting themselves deeper in the mire. Kate refused to answer because she didn't know how Gerry would reply when he was interviewed. Innocent people would have answered EVERY Q ...nothing to hide ,nothing to fear.The whole shambolic case is nothing but lies and spin dished out by Mitchell. Why? Who knows.What are they all hiding and who is protecting them all ?