I know that, in the end, it doesn't even matter who originally caused the destruction of the city, but I'm still curious. I really only got to explore a couple people who propably weren't the threat before I got interested in the whole immaculate armour business to get down in the underground tunnels and find out how to stop the law.

So here's what I think:

After you get the perfect ending, Altrius tells you the Jarl was overthrown and executed after Ulrin found out that his wife was held against her will by Metellus. There's no reason for that not to happen if you weren't around, right? So was it Ulrin, breaking the law by killing the jarl?

Or maybe it was even simpler and it was just those bandit/dark brotherhood dudes who show up after you talk to the jarl. Without you around they could just get into the city, steal/kill something -> laser robots.

Am I in the right direction or is there some darker scheme at hand that I completely overlooked in my playthrough?