Acting as a Liar

I recently viewed the 1997 film Deceiver, which I had never heard of before but was recommended to me (based on my previous murder mystery/deception viewing) by Netflix. The film stars Tim Roth as an overprivileged epileptic alcoholic liar accused of murdering and cutting in half a call girl, and I initially expected it, based on the film's tag lines and first ten minutes, to be the portrait of a deceptive serial killer. Instead, the identity and intentions of the murderer (Roth's character?) are further and further confused, leaving the viewer with no confident grasp on the truth, even at the end of the film. What particularly struck me, more than the plot or (quite captivating) cinematography of Deceiver, was the similarity of Tim Roth's character to that of Dr. Lightman, Roth's more recent television character on the now canceled FOX show Lie to Me. In both the film and TV show, Roth uses his powers of deception to root out the deception of others, and in both he is somewhat creepy yet oddly alluring. The similarity between the two roles makes me wonder what Tim Roth is like in real life, and what makes him particularly suited to play this type of character. Can we pretend to be liars if we don't actually lie, and does pretending to be liars actually make us liars? Is acting one of the honorable reasons to lie, like deceiving criminals to get them to confess or telling a child Santa Claus is real?