I don't know the burden-of-proof standards of the International Court of Justice - preponderance of evidence vs. beyond reasonable doubt, etc. - but Brenus is pretty much right. Although intent in the handling of the missile doesn't go very far, since you don't have to intend to commit an atrocity to be guilty of having committed one.

However, the firing of the missile itself may not even be relevant to the case or jurisdiction, which seems to be a Ukrainian suit that Russia is

...intervening militarily in Ukraine, financing acts of terrorism, and violating the human rights of millions of Ukraine's citizens.
The document accuses Russia of violating the 1999 International Convention for the Suppression of the Financing of Terrorism by supplying money, weapons, training, and other support to separatists in the self-proclaimed Donetsk and Luhansk People’s Republics in eastern Ukraine.

It also says Moscow’s treatment of Ukrainian and Tatar minorities in Crimea breaks the International Convention on the Elimination of All Forms of Racial Discrimination (CERD).

Ukraine is demanding compensation for what it calls terrorist acts committed on its territory, including the shelling of civilian areas and the shoot down of Malaysian Airlines flight MH17.
So on its face Ukraine has a good chance of getting at least some charges to stick.