Yeah, about that. This is a feudal future*. Are you seriously going to conduct interviews with peasants in enemy occupied territory?
Uh... yah doy!
You just attacked the personal retinues of the de facto head of the Imperium, a body to which you are nominally loyal. This de facto head also controls the intelligence agencies. You did this in front of millions of witnesses. You don't think that she wouldn't be able to round of one or two hundred credible ones? It's not like feudal societies were above letting imprisoned felons testify when they wanted to (see the trial of Joan D'Arc) but there's probably plenty of lesser nobles who would make fine witnesses for the events.
Of course all of this is just sort of a side detail because this takes place in a sci-fi setting where there are electronics and holo-recordings. Or that there would be rubble spread out through the system bearing al-Malik colors and markings. Or that a couple years later the events would be witnessed by telescopes in other systems. This isn't something you could plausibly deny happening.
I don't even know what the point of arguing this is anymore. Does anybody actually have the slightest bit of OOC doubt that Azthor did this? If he wants to say that IC he demands and appeal to the imperial courts and dragged the case out for decades I'm fine with it. But I should be entitled to show people OOC proof of what happen if they actually doubt it, just like Azthor used OOC proof of my messages to him.