As we are learning about the massacres in Bucha, it is becoming apparent there are two camps in receiving this news on the world stage:
It's real, it happened. This is certainly Ukraine and the West's position.
Fake news, staged, never happened. This has been Russia's position. Probably will be that of its supporters as well.
The camp of neutral countries, who can be expected to bear witness is limited. For example, Switzerland would have been a natural choice, until last month.
The ICJ can investigate, but even if the investigation or its finding doesn't get vetoed, the capability to bring senior Russian politicians to justice is very limited in the near and medium term (even a changed Russian government would find it politically awkward to ship off Putin).
Article 94 establishes the duty of all UN members to comply with decisions of the court involving them. If parties do not comply, the issue may be taken before the Security Council for enforcement action. There are obvious problems with such a method of enforcement. If the judgment is against one of the permanent five members of the Security Council or its allies, any resolution on enforcement would then be vetoed.
Another aspect is that neutral coverage on the ground is limited, if you look at coverage in press like India's:
"All the photos and videos published by the Kyiv regime, allegedly testifying to the 'crimes' of Russian servicemen in the city of Bucha, Kyiv region, are another provocation," Russia's defence ministry said in a statement.
It called the footage "another staged performance by the Kyiv regime for the Western media."
Reuters was not able to independently verify who was responsible for killing the dead residents.
But three bodies seen by Reuters reporters on Sunday -- the corpse with the hands bound and two others which did not have bound hands -- bore bullet shots to the head consistent with what Bucha mayor Anatoliy Fedoruk and his deputy described as executions.
How can the truth of what was observed best be preserved now for the future, using as much as possible, sources that can't be claimed to be siding for one side rather than the other? To take an example, a Serb nationalist can claim Srebenica never happened and that sanctions against Serbs are just bigoted bullying. How can this be documented in the least-deniable fashion?
How can you get people who really really can't be argued to be "Western stooges" to certify what they've seen, first hand?
To clarify: this is less about swaying public opinion, future political penance or criminal investigations now than it is about laying a solid groundwork towards gathering as much neutrally-sourced evidence first hand as possible, while the crime scene is fresh.