As I understand it, around 80 bodies have not been accounted for, that would be more important to clear up than the evidence of the missile attack. I believe they have sniffer dogs on the job to locate the bodies or parts thereof.
I don't think the issue of what brought down the plane is in doubt, everyone seems to believe it was a missile and there is little choice in who fired it given the locale. In any event, local militias are not necessarily expert in examination of debris, there may be plenty left behind.
An examination of the missile parts might have revealed exactly who supplied it? I'm not optimistic that they will find a lot of the missing bodies given the large spread of the debris area and the time passed but out of respect for the families of the dead it's good that they're having a through examination of the area.
Anyway, they've been on site for a few days now so we'll see what comes of it.