There is no right answer to this conundrum simply because there are too many variables.

-Some policemen will be honourable sticklers for the rules and would never interpret silence as a sign of guilt.
-Alternatively, some take the default position that silence = something to hide.
-Some are masters of language and will twist what little you have or have not said to make you squirm and say more.
-Plus you never know what other people are saying, are they making a liar out of you?

Rather than try to answer an unanswerable question, it would be better for people to be more educated about how law enforcement works so that they can make informed decisions should they find themselves in a situation where a policeman is asking questions.