If indeed the Russian militants are on the site sweeping for evidence, you can bet that evidence tying them to the missile will go the way of Lois Lerner’s hard drive. Lois...pick up the white phone,...you’re needed in Donetsk.
The dispute is over who owned the Buk that did it, and there will be no evidence at the crash site.
What we do have is independent confirmation from AP reporters that the terrorists have a Buk, and one of the main terrorists himself gleefully announced at the time that the plane went down that his guys had just shot down an AN-26.
This was pretty clearly the work of Russian terrorists, and there is little a scene cleanup can do.
The fact that they control the scene is more evidence against them, not less.