Hi Mike, what has lead you to believe this?
He was away from the tapas bar, when Maddie went missing, and his movements after she was reported to be missing leave a lot to be desired. Additionally, he appeared to be eager to know the whereabouts of Kate and the children, whilst Gerry was playing tennis, and he was at apartment 5A the children were getting bathed and ready bed...
Additionally, I think it was he who persuaded the McCanns to holiday at the resort, he having previously spent time on holiday there...