Images. reporter: even as russian troops mass in eastern ukraine for what the u.s. believes will be a huge offensive, authorities in kyiv continue digging up bodies. painstaking work that goes hand in hand with investigating russia s attack on kyiv and possible crimes committed by vladimir putin s invading troops. prosecutor general iryna benedictova is leading the charge. she spoke to me at the edge of a mass grave in the suburb of kyiv. for us the motivation is justice. and of course we understand that all the ukrainian want fast justice. true and fast justice. that s why we do everything to document all evidence, all facts of war crimes that we have here in ukraine. reporter: french forensic investigators are now also on the scene, not because ukraine lacks expertise, but because