But after listening to several other lines of dialogue, learning more about the laws involved, and observing a few other events, I’ve concluded that Tullius was almost certainly both aware and guilty of the Last Dragonborn’s attempted murder. Here’s what led me to that conclusion:
1. General Tullius probably MADE the list.
For the list the LDB wasn’t on to exist, someone must have written it. The most likely candidate for this role is the mission’s commanding officer: General Tullius.
Even if he didn’t make the list himself, he should’ve at least been aware of who was on it, so he shouldn’t have needed Hadvar or the captain to tell him the LDB wasn’t on the list.
2. Tullius knew the LDB was there.
If you speak to him in Castle Dour, and tell him that you’ve already met/you were at Helgen, he’ll comment that you were “One of the prisoners, if I recall correctly.”
So not only was he aware of the LDB’s presence, but he noticed them enough to recognize them days, weeks, or even months later. And yet, even if they looked nothing like a Stormcloak, he couldn’t be bothered to say, “Hold up, who’s that and why are we killing them?”
3. The LDB wasn’t charged with a crime.
In the aforementioned Castle Dour conversation, upon being satisfied that the LDB is there to sign up with the Legion, Tullius says, “I’m sure your being imprisoned was all a terrible misunderstanding.”
In other words, he had NO knowledge of any crimes the LDB had committed. He didn’t offer a pardon, or demand that they pay off their bounty; he simply acknowledged that they’d done no wrong that he was aware of.
If he had no reason to believe they were guilty in Castle Dour, then he had no reason to believe they were guilty in Helgen. He just couldn’t be bothered to find out whether or not they were.
To Tullius, the life of a potentially innocent person simply wasn’t worth the bother of finding out whether or not they’d even committed a crime, let alone one worthy of death – not that a crime’s worthiness of death matters to Tullius, given that…
4. Look who else was on the list.
According to Imperial law, as outlined in the book Legal Basics:
“Any act of stealing, taking, or, without explicit written or verbal permission (or what a reasonable person would infer as implied permission) an item or items from a person, group of persons, or entity a reasonable person might assume to be sentient's place of residence, business, person, or other location a reasonable person would assume is secured from looting. The punishment for this crime may include a fine or incarceration, or a fine and incarceration.”
And yet, Lokir, a horse thief, was on the list to be executed. No other crime of his was mentioned, so it seems that Tullius knowingly sentenced a man to be killed for what a Legion general should have known was a crime worthy of a fine and/or incarceration, not death.
5. This isn’t Tullius’ only questionable execution.
Roggvir, the man who’s executed when the LDB first visits Solitude, claimed that Ulfric’s killing of Torygg was no murder – Ulfric challenged the High King to ritual combat, which was legal in Skyrim.
His claim is supported by Sybille Stentor, who’s firmly against the Stormcloaks’ goals. She acknowledges that “By Nord custom, once the challenge was issued in court, Torygg had no choice but to accept. Had he not, Ulfric would have had cause to call a new moot and a new vote for High King.”
She claims there was “no choice,” but in reality, Torygg had a choice: he could have refused, and allowed the moot to choose a new High King. He chose his career and his honor over his life, and consented to the duel.
Whether the way Ulfric won the duel was honorable or not is a subject for another discussion. Killing Torygg instead of incapacitating him was, in my opinion, unnecessary and therefore wrong, but that doesn't change the fact that the High King recognized the legality of the fight and consented to it.
Therefore, the duel was legal under Skyrim’s laws, and by extension, so was Roggvir letting Ulfric leave.
Now, there is some ambiguity as to whether Roggvir’s execution was ordered by Tullius or Jarl Elisif, but given Elisif’s kind nature and Lokir’s execution by legionnaires, Tullius seems like the more likely candidate.
One could argue that the duel, while legal under Skyrim’s laws, was illegal under the Empire’s. But Tullius didn’t declare the duel illegal. He simply pretended it never happened, and had Roggvir killed under false pretenses.
All in all, the Last Dragonborn's wrongful near-execution wasn’t one-off mistake.
It was part of an ongoing pattern of questionably legal executions, ordered or knowingly permitted by a man who almost certainly knew that the random traveler who wasn’t on the list was about to be killed, but who couldn’t be bothered to find out whether they or his other victims deserved to die.