In the case of MH17, there were strong indications it had been shot down within days at most, and once the Russian-backed rebels let investigators into the area, one found pieces of wreckage showing shrapnel damage. Hardly consistent with a defect in the airplane.

Official doings take time; if I went out in the street and killed someone in plain view of lots of witnesses, it would still take years for a final verdict to be passed in the courts - yet there would be no doubt as such as to what had happened.