Perhaps rather than calling someone a liar one might use say:
"If the alleged facts (and/or statements), uttered or reported to be uttered, by one Mr Schicklegroover are contradictory to the truth of such matters and if it is shown that Mr Schicklegroover knew of such inaccuracies, one might reasonably draw the conclusion that Mr Schicklegroover has knowingly uttered false statements that may well be the detriment of others.
