In 2005 the Graduate Center in New York City sponsored a conference titled "Picturing Atrocity: Photography in Crisis." I was able to attend several of the sessions and found them fascinating. One of the highlights was Alfredo Jaar's work in the second session. There was also a review of the conference written up in Afterimage. Now the full sessions are up online in streaming video, hosted by the University of Leeds.
I highly recommend reading the Afterimage article and then watching the sessions.