The head of the ACLU suggests that Obama formally pardon torturers if he does not prosecute them, as a way to affirm that what they did was a crime.

While I see his point, I doubt it would achieve the goal very much. Any torturer that could potentially be prosecuted, either in the US or by an international court, should not get a pardon. The ACLU points out that there is no statute of limitation for many of these crimes.

Some of those responsible may be prosecuted in other countries or in the ICC.