Unfortunately, I can only find some sound bites of the speech of the Russian Ambassador to the UN SC, Vitaly Churkin. However, those words are to a large extent similar to an official press release by the Russian Embassy in Malaysia. Hence, I will use the statements from that press release as the Russian arguments for their Njet are quite interesting.
"Russia is interested in a comprehensive, accurate, independent and transparent international investigation of the catastrophe of Malaysia Airlines Flight MH-17". Why? There were no Russian casualties and the incident happened on Ukrainian soil. Formally, there is no Russian involvement.
"There are many serious questions concerning the organization and conduct of the investigation." By whom? The only questions seem to come from Russia. This does not make any sense given the aforementioned lack of Russian involvement in this incident.
"Russia has been insisting on making the investigation transparent, first of all, with respect to the UN Security Council." Why would Russia insist on this when there is a lack of Russian involvement?
How would a Russian comprehensive, accurate, independent and transparent investigation look like? The best example to me is the murder of the Russian politician Boris Nemtsov on 27 February 2015. Interestingly, his murder may even be (in)directly connected to the situation in Ukraine. According to the Ukrainian President, Boris Nemtsov was preparing to reveal his evidence for the Russian involvement in Ukraine (Inquisitr, Economist). The murder investigation on Boris Nemtsov (Forbes, FT, Politico, Telegraph) clearly shows how Russia would deal with a politically sensitive investigation like MH17.
Interestingly, Leonid Bershidsky claims in Bloomberg View that Russia's "Njet" is merely related to America's "No" on extraditing its citizens wanted for crimes committed elsewhere.
"I cannot forecast to you the action of Russia. It is a riddle wrapped in a mystery inside an enigma: but perhaps there is a key. That key is Russian national interest". Winston Churchill.