Concentrating on what happened to who and why is not helpful in resolving disputes.
Instead, concentrate on how that action or lack of action made each party feel and help them discover how their feelings shaped the perceptions they built up of one another.
When we stand in each other's shoes we can realise that our actions caused the other person to believe something (that we didn't mean or intend). We can then start the journey towards understanding how we got in the mess in the first place.
Understanding the causes of our misperceptions gives us a powerful start to build better strategies for our future.
Just stop and ask 'Why do you/I think that?'