A problem they faced with old Milo was that it wasn't possible to pin anything on him.
He was in charge mostly with Kosovo; but the hundred thousand dead bodies (quoted by Clint) didn't actually pan out.
Bad things happened in Bosnia, etc.; but in areas outside of Milo's control. There are some real war criminals there (on both sides, although the west took one side and the other is on trial for war crimes); but Milo had no direct power there.
Milo did the Hague a favor by dying, as they could never pin anything real on him and it was starting to become embarassing.
Still, he should have plead guilty of mass murder genocide, just because he'd be out of jail by now. I mean, does anyone actually spend 6 hears (how long his trial has taken) in a European jail any more?