Perhaps there are DNA samples from known persons (eg Cylon or his supporters?) that these samples could be compared to, in order to infer their likely political affiliation during this time of unrest? Or maybe they just want to confirm that all the bodies were definitely Athenian or Greek as a means of determining whether they were foreign hostages or domestic political prisoners of some kind?
I found a couple articles on this (the Phaleron mass grave site has been in the news for a while): http://www.forbes.com/sites/kristinakillgrove/2016/03/24/arc... , http://www.livescience.com/54432-mass-grave-unearthed-in-gre...
But none are specific about what it is that DNA studies would hope to confirm/deny or inform, or how exactly they'd do it.