I think you're underestimating the bravery (or possibly stupidity) of the Nords. If you use the Voice on them, they fight right back. They also fight back when Ulfric uses the Voice against them in the Battle of Solitude. In both of these cases they have the option of running away, an option that's infinitely better for their livelihood.
Here's another case to consider. When Alduin attacks Helgen, it's the first time any of them have seen a dragon, something that's definitely more intimidating than Ulfric Stormcloak. Yet, instead of running away en masse, you can see a lot of them fighting back or trying to get the townspeople to safety instead.
Wow, lots of discussion happened in the last several hours!
Roggvir is quite clearly a Stormcloak sympathizer, so it's certainly easy to see how he could be implicated in an escape. The problem is how illogical an actual escape is in the first place. Since we don't know all the details, it's impossible to say for certain, but Roggvir could have known Ulfric came to Solitude to murder Torygg and somehow sabotaged the gates to ensure his escape (thus being the only guard responsible). In this circumstance, Ulfric could have been pursued by guards when he reached the city gates. However, this is all wild conjecture with no evidence.
With the only evidence we actually have to go by, Roggvir is simply a man known a little too well for his sympathies whom the Empire used to avoid blaming the court and palace guards for letting Ulfric leave after a lawful duel according to Skyrim's customs.
I've been trying not to be such a @#$% when it comes to civil war stuff, so I rejected the first five or so responses I thought up. Here's the sixth.
Roggvir is an adult who, to all appearances, seems to be sound of mind. This means that he's fully capable of understanding things like the laws and traditions of his homeland, and of interpreting his responsibilities to both them and his fellow citizenry. Thus, I believe that none of the options that you present are correct. You give him very little credit, essentially painting him as either a traitor culpable for crimes he didn't commit or a witless dupe who didn't understand the ramifications of his actions.
Roggvir clearly knew what he was doing when he let Ulfric escape from Solitude following the duel with Torygg- while before the block, Roggvir asserts that Ulfric challenged Torygg and beat him in fair combat. Even if he didn't know exactly how it happened at the time, he's presumably had enough time to learn the details...and he still defends Ulfric. From his point of view, he was helping an innocent man escape from those who sought to punish him for a crime that didn't actually happen. ("There was no murder!")
Roggvir had a choice about whether or not he personally believed Imperial law (which considered Ulfric's act to be murder) or Skyrim's traditions (which saw it as a lawful duel) were more important...and he chose tradition.
Did Roggvir deserve to die? Hmm...
But Ulfric committed a murder, at least according to the Imperial Legion*. Helping a murderer escape is aiding and abetting a criminal. If Roggvir knew Ulfric killed Torygg, he is aiding and abetting a murderer, a traitor, or both. So yes, if he was aware of what happened**, his execution is justified by local law, because he assisted in a crime and didn't choose to, say, flee to Stormcloak territory himself.
I don't get the point of your strawman arguments about things like doctors treating patients. Can we just pretend you never said that?
*Though the whole of Solitude seems to agree, whether only to play along or it being their original opinion we can't say.
**But how would he be? Faintly hearing the Thu'um on the other side of the city wouldn't tell you that the High King was just killed in 'fair combat', it would just tell you that something that sounded like thunder just happened out of nowhere. People in Ivarstead comment on hearing distant thunder from The Throat of the World, but in a bustling city there would be quite a bit of background noise compared to a sleepy little farming village. So, did Roggvir know that Ulfric had killed the High King? Again, there is no evidence anywhere in the game that he was an agent of Ulfric. He was a Talos worshiper (and clearly outspoken about his Stormcloak-ish beliefs), so he would have been likely to aid Ulfric without even realizing what he was getting himself into. Also, the idea that the guards would have been 'shocked' by Ulfric using the Voice is absolutely absurd. His study at High Hrothgar is a known fact, and it's unlikely he went through the Great War and the Forsworn Rebellion without exercising battlefield use of shouts.
That part is specifically in response to Borommakot's question here, about whether or not Roggvir is culpable for any and all lives lost in the war following Ulfric's escape. I don't think so, because, while he may (and I do not believe this) have allowed a murderer to escape, he's still not responsible for either Ulfric's actions or the actions of everyone else involved in the war.
Oh, see, now that I know who you're replying to it makes slightly more sense. But it's still quite the strawman to throw examples like that out. A better example would be a vet treating a bullet wound and keeping it on the down low, then finding out later the guy he treated was involved in a firefight with police and killed an officer.
First, aiding and abetting is not the same as being a murderer, which is something several people have charged in this discussion.
Second, my point is that from Roggvir's point of view, Ulfric is not a criminal - thus, helping him does not make Roggvir himself a criminal. If you assume that the only way to view this is "Ulfric is automatically guilty, therefore does helping him make you guilty or not," then you've already biased yourself toward the Imperial position...in my opinion, a mistake.
Third, my "strawman arguments" were a response to this, not to whether or not Roggvir is personally guilty of the crime to which he is accused. And while I may regret things I say, I will never erase them - if you're going to say something, have the minerals to either defend your position or admit you were wrong. I choose the former.
Fourth, I don't even know what you're trying to say here. Roggvir heard Ulfric shouting? What? I think you're bringing up the "Did Ulfric 'cheat' when he used the Voice?" argument, but I've made it pretty clear I consider that irrelevant. I believe the fight was "fair" in the sense that Ulfric challenged Torygg and Torygg accepted, thus - under the ancient law of Skyrim - anything Ulfric did to kill Torygg was legal. It's only by applying Imperial law that the act becomes murder, because the Empire doesn't recognize the concept of a legal duel to the death.
I already figured out who you were replying to. Did you not read anything posted before you replied to this?
On the fourth paragraph, I'm going over the idea people seem to have that Roggvir would somehow be aware of everything that happened clear over at the Blue Palace, without knowing it was going to happen ahead of time. This is ludicrous. If word of the goings on had traveled faster than Ulfric was able to flee the city, he would have faced a mob of angry citizens on the way out. Clearly he got the hell out of dodge and reached the gate before word spread throughout the city. Thus, if he was not an accomplice to begin with, the most Roggvir could have known was that something sounding like thunder happened on the other side of the city. That's insufficient knowledge to be aware of the implications of opening the gate for Ulfric.
I actually started typing the long post, then responded to Golden Fool, then went back and finished this one. So, technically...both?
If he didn't know what happened, then wouldn't that make the Imperials wrong for executing him? Also, I don't believe that's true. He doesn't say, "I didn't know what Ulfric had done!" He says, "There was no murder! Ulfric challenged Torygg. He beat the High King in fair combat. Such as our way! Such as the ancient custom of Skyrim, and all Nords!"
I've been arguing for the Imperials being wrong for executing him.
Also, something nobody's touched on is how long it's been since the incident. While we don't have an exact date, I fuzzily remember Hadvar mentioning that Tullius has only been in Skyrim for a few months, and even more fuzzily remember someone or other saying the civil war intensifying was the reason Tullius came to Skyrim in the first place. That would make the delay between Roggvir's fateful actions and his execution measured in months. Never mind the convenience of the execution happening right when the LDB shows up, as that seems to happen to everything everywhere we go. But clearly Roggvir could have protested his innocence at first, but long since given up on it, if it's been months since the incident! He's also probably a much more loyal Stormcloak supporter now, whether he was initially culpable or not. Thus, we can't really glean anything meaningful from him not protesting his innocence after months of imprisonment.
That would have to be some absolutely amazing work by Tullius! Showing up because he got word the High King was killed, gather enough intelligence to locate Ulfric, and set up an ambush for him in a matter of days? And all this with Ulfric having an obvious head start due to the delay of news even traveling outside of Skyrim.
Sorry, I just don't see this as possible.
My impression was that it was several months, at least. The rebellion didn't happen in earnest until Torygg died, which means that there had to have been time for the news to travel to every corner of Skyrim...but not so long that the people of the Blue Palace aren't still mourning.
As to where Ulfric was going...I don't think it matters? Skyrim is a big place and he's running an entire rebellion, presumably he just had some business somewhere that required him to personally show up.
You're assuming that Roggvir would have wanted to prevent the war. Ulfric certainly knew what he was doing, and if Roggvir was informed enough to believe he was doing the right thing by letting Ulfric go, he's likely informed enough to realize what's going to happen...yet he still did it. The Stormcloaks view the war as a necessary evil at worst, a righteous crusade at best; if Roggvir supported them, he's likely to have thought similarly.
Who gets to decide when something is justified? The Empire? The Stormcloaks? You? Me? Maybe this is just another argument that can't be solved, because it's all about perspective and opinion.