They would probably consider the population casualties a fringe benefit.

That's sort of the rule of thumb of how any trial should go: let the defense make up most of the rules (within reason), and then when it tries to appeal later, just point to where either both parties agreed to a rule, or where the trial judge let the defense make the rule to begin with, and then say "so, what's the problem exactly?"

I haven't been keeping up with it, but I do remember something to the effect of there was video evidence that easily overcomes his defenses, and his response to that was to say it was inadmissible as evidence.

Historically, it's because it changed air travel. Airships were converted to using the non-combustible helium instead of hydrogen almost instantly.

But even that point aside, like the titanic, like the supposed war of the worlds riot, like the great fires of Chicago here and London over there, each great catastrophe gets one chance to completely knock us senseless. It's only by the subsequent ones that we start going "yeah, I knew that was possible. Wonder why they didn't prepare?"

Minor historical nitpick here, but the audio you're referring to was a radio broadcast. Moving pictures didn't have sound in those days; someone else just paired the two together later.