How can you know that someone is contrite?

For the last few weeks my ethics students have been studying forgiveness.  One of the persistent questions about forgiveness is whether, in order to be forgiven, one must first be contrite or repentant.  (We have not been speaking of the idea of God forgiving people; we've limited our discussion to the possibility of people forgiving other people.)

I have to confess that this posting was prompted as much by my viewing, last night, of Battlestar Galactica as by our readings.  In season 3, Laura Roslin calls for a Truth and Reconciliation Commission (like South Africa's after Apartheid) after some human-on-human atrocities.  That got me thinking once again about Desmond Tutu and Simon Wiesenthal, and their respective books on forgiveness.

The easy answer to my question is to say that one does not need to be contrite to be forgiven.  This is easy, but not simple, because it raises other questions about the nature of forgiveness.  And it brings along with it the possibility of depriving someone of their moral agency by denying the reality of their choices.

Most of us are inclined to give the opposite answer, namely that it does not make sense to forgive those who are not sorry for their offenses.

But this raises another difficulty: how do we know when people are adequately sorry?  Additionally, does this position make it more likely that we will forgive those people who only seem sorry?  What if someone has expressed their contrition to the best of their ability but we have not been able to perceive it, for cultural or other reasons?  What if someone is not at all sorry, but has made a convincing public show of contrition?

What do you think?