Doctor Martin Roberts Has Written Numerous articles on missing Madeleine McCann, his latest here.
"Three may keep a secret if two of them are dead."
Already a century-old before Benjamin Franklin utilised it, this proverb still carries some weight, although there are less dramatic options open to us these days, e.g. 'three may keep a secret if:'(a) one is your local Catholic priest and the other his CardinalOn March 19 this year the FOI News reported thus: link
or
(b) one is your country's overseas Ambassador and the other resides in the Foreign and Commonwealth Office.