If Russian special forces which are doubtless in large numbers 'close to the scene' were ordered to make that crash site available to recover bodies the irregulars would not dare intervene.
That's not exactly true and shows that the West is again looking at the whole thing through the prism of their fantasies about Ukraine, and not realities on the ground.
Kiev government took power through a coup, was opposed by most of the population of the Eastern Ukraine. Almost entire military in Eastern Ukraine rebelled against Kiev, and they have all the equipment that Western Ukraine has. What's more, Kiev had to pretty much build the leadership and new army (national guard) from scratch because most of them were Russians opposing Kiev and part of the problem was that cash-strapped Ukraine was not paying the soldiers for months.
The only reason the rebels were not using SAMs before was because it took Kiev a lot of time to reassemble something resembling an air-force - the rebels had nothing useful to shoot at.
It was totally childish by the West to treat the insurrection in Eastern Ukraine as bunch of drunk losers with peashooters and not trained military force equal to that of Kiev. Their equipment and training is at least at the level of Kiev forces. The fact that Kiev forces were scoring some victories lately (marked with heavily shelled towns) shows that Putin was actually bowing to pressure and stopped supporting the rebels in meaningful fashion. So, ironically, he probably is in this mess because he unplugged the rebels from C&C support.
BUK system is intended as completely mobile platform intended to secure air-space for advancing tanks and rest of such toys. It can operate as part of integrated system, but its chief purpose is being an autonomous weapon protecting advancing columns on the ground. Interestingly, even Russia does not have effective countermeasures/control of BUK because they lost some of their advanced planes in Georgia because of BUKs smuggled from, (where else?) Ukraine.
p.s. In today's speeches, Ukrainian politicians demanded advanced weaponry from the West so they can finally "bring order".