I am afraid that both of these statements are false. Even if there is a serial number, I have not seen anything linking that with Kramatorsk nor Ukraine. I have however seem a number of geolocated pictures of missiles launches from Shakhtarsk happening on a daily bases.

Re evidence and burden or proof, I am afraid you controllers would need to provide the world with evidence that that missile come from someone else. I know that your aim is to create doubt, but, on this case, the reason for hitting a train station, the fact that missiles are Putin's weapon of choice for strategic large targets and the fact that if Ukraine would ever choose a false flag would be a civilian target but certainly not a real strategic target that is critical to evacuate and send over reinforcements makes the case very clear:

Putin's army does not care if there are civilians or not - the will hit any target they consider necessary. It is more of a grinding machine than a human led army.