To summarize: answers to some questions stil being bandied about here
As to whether the plane was brought down by an SAM
from Angels
A Buk launcher has been seen in the locality from where the missile was fired. Look back on this thread, there are pictures, one from a reputable news agency AP), also video. Today a Buk launcher, minus at least one missile, is seen being driven from the vicinity towards the Russian border along a route Russians have used before. See my earlier post.
Additionally every square meter of this area is covered by military spy satellites 24/7; not only is Washington firmly convinced it was a SAM but Moscow has not offered any alternative theories so likely they are also certain.
As to who:
MAINJAFAD with the experience with these mobile SAM systems has explained very clearly in two posts that the system is highly automated and does not require highly sophisticated personnel to operate it -it is a mobile field system, thus that makes the eminent sense (IMHO)
it is very likely that there are plenty of ex Soviet / Russian / Ukrainian armed forces personnel about on the rebel side who could operate this system to a standard that would allow an aircraft at 33,000 ft to be engaged.
So the separatist/rebels likely being run by the GRU and why? Because they could, they only knew it was a plane and being an undisciplined group of likely not very bright wannabe 'warriors' it never occurred them that before you shoot something down it would be the very good idea to determine if it was civilian or military -and whose I might add; they might have just as easily shot down a Russian plane.