I wouldn't be naming the specific examples as that might (will) needlessly divert the attention away from the question itself.
Let us say I am trying to research about historical events in a region. That events have multiple narratives given by parties that are stake holders. Some vehemently deny accusations while others make repeated accusations. I know it is really about tracking the evidences as one might find in documented/published material, but this is where the problem lies.
Most of the documented instances come from one of the parties involved, which makes it hard to consider. Furthermore, the narrative of a party is consistent with the published material, which must not be surprising.
There are very few so called "neutral" parties that have published anything substantial.
How should I proceed now?
I am a student of neither history nor journalism, so it would be helpful if additional information is provided regards methodology.