The maps you're linking to further implicate the rebels (see again the video reconstruction, which illustrates the trajectory the missile took from its launch site, which is not the same as the crash site, placing the missile launch even further from areas of Ukrainian control and even closer to Russia.)
Further, to even entertain this question, you have to believe that Ukraine positioned BUK launchers in the most heavily contested part of the country, in areas which were apparently held by rebels just weeks earlier.
This does not look like a serious controversy. The rebels shot the plane down.
You ask why the report doesn't say who fired the missile. The report explains why. You are right: the report does not say who fired the missile. It merely makes it obvious who did.
Further, to even entertain this question, you have to believe that Ukraine positioned BUK launchers in the most heavily contested part of the country, in areas which were apparently held by rebels just weeks earlier.
This does not look like a serious controversy. The rebels shot the plane down.