It is impossible to prove a negative.

This means that you cannot disprove something- it is impossible to do so.
One cannot say "unicorns exist" because there is no proof that they do not exist, that is futile.

So, until conclusive evidence of a magical man flying through the sky (who created himself, somehow, and also created robbers, murderers, and sinners) is found, there is no god. Guilty until proven innocent analogy.