In approaching this situation, there would be a few steps I would take first:
Speak to the person who made the report briefly about the important details.
Check if either person is in a roleplay situation.
If not, teleport them both to a secluded area/roof.
Once this is done, I would first explain Player X's side of the story to Player Y, then ask for theirs. I would weigh up both sides of the story, use the information provided to me in the logs, and come to a conclusion on what seems most logical. I would explain this conclusion to both parties and if either of them denied this, I would require proof. If Player X could not procure valid proof or Player Y procured counter-proof, I would be forced to end the situation and return each party to their original positions. If Player X procured valid proof or if Player Y admitted to RDMing Player X, I would speak to and warn Player Y, then return each party to their original positions.