Do you wish you could have stopped the execution?
The very first time I walked into Solitude I walked up to the executioners and got too close to me so they attacked. I killed them, fled and reloaded.

To put it in retrospective, you are a security guard in a bank. A senator or mayor of NYC walked into the bank. He then cashes in a fake check in Obama's name for 1 trillion dollars and walk out of the bank. This is YOUR job to stop him when there is not so much as a sound from the bank manager and bank president?
Security guards observe and report and are meant to deter by their presence. They do not intervene...a COP would've been a better exmaple.
Frankly, I find death to be a prefrable punishment to long-term imprisonment, even in our world. I'm probobly in the minority in that view...
So am I.

I wish you could. It doesn't matter what you do, you can console kill everyone responsible for the execution and Roggvir will just drop dead of his own accord.

Now, I don't feel so bad. ...and now that you mention that I think I saw Roggvir's head just rolled off without action from the NPCs.

I chalked it up to lag.

The city guard wasn't executed because he let Ulfric out, he was executed because he let him IN without orders to do so. Clearly as a setup to force a duel.
"in" is how I understood it too.

From what I've heard ingame: Any jarl sitting (read slouching

) on his/her throne must accept a challenge to a duel. So no laws broken.
I doubt jarls from any of the holds are forbidden from entering other holds. This would be cowardly and un-Nordlike and probably against protocol.
Ulfric capitalized on the above tenets by challenging a jarl he knew he could defeat (Ulric admits he knew he could defeat Torygg to us in one of our conversations) so he kinda' loopholed himself into the situation, but broke no laws in the strictest sense.
Since I believe the challenge protocol and doubt jarls are forbidden from visiting, Roggvirr broke no laws by letting Ulfric in or out since Ulfric broke no laws and therefore shouldn't have been detained. If anything, the Empire was violating Nord laws/tradition by trying to prevent a non-puppet jarl into Solitude for a duel they suspected Torygg would lose.
Most of our laws are based on tradtion so you can't dismiss tradition with a clever statement. It was tradition to not murder, rpae, and steal in human socities long before any codes of laws had been transcribed.
Edited for usage.