Summing up
It's hard getting an overall picture from all the conjecture, and, lets face it, propaganda written here. Here is an attempt at a summary of the facts and evidence we actually have so far of the crash itself:
1) MH17 crashed, apparently shot down by a SAM.
2) President Obama states the US has intelligence that it was shot down by a missile provided by Russia, but provides none of that evidence.
3) Reports state that the so-called "pro-Russian militias"* have acquired Ukrainian AA regiment(s), including up to 100 BUK missiles. This ties in with the fact that the Crimean and eastern Ukraine population is predominantly Russian-speakers, and pro-Russian, so that when seceding, any military installations in the region would most likely immediately fall into "rebel"* hands.
4) The Russian MoD has held a press conference showing evidence that
- the Ukrainian military had maximum radar activity and an AA installation in the area at the time of the crash,
- MH17 changed course just before crashing,
- there was another unidentified military aircraft in the vicinity of MH17 when it went down,
- social media pictures of an AA vehicle fleeing the area afterwards had the wrong type of armament, and was not in the city it was claimed.
The Russian MoD also asked the US to present its evidence, and stated clearly that Russia had not supplied arms to the so-called pro-Russian militias*.
5) The tail of the 777 broke off in air, and the main part of the fuselage fell with both engines still attached, and fuel tanks apparently intact.
6) Photos have been published showing damage apparently caused by shrapnel/fragmentation of AA weapon, to a part of a wing and the port side of the 777 cockpit.
7) There has been a leak that the US intelligence actually implicates the AA installation responsible was manned by Ukrainian troops, possibly lacking discipline, rather than "pro-Russian rebels"*.
* the political reality in Ukraine at the moment is complex and confused. Labels given to groups participating in the conflict tend to reflect the writers' opinions rather than the truth on the ground.
I think I have summed up all the hard evidence we can count on at the moment, though I would welcome being corrected.