I'm not entirely sure if this is my jurisdiction, but here's my thoughts so far on reading, rereading, and thinking about it.
I think if I was presented with all the evidence that has been posted in this thread, I think I would have agreed that Yahir should have been arrested. It seems to me that there was far and enough evidence to take him in on probable cause. From there would be a drawn out legal battle, assuming he didn't confess under pressure (most people do IRL anyhow). In who knows how long, following a process of discovery, depositions, legal scrambling, there would finally be a trial where he might or might not be guilty. The entire duration of which he would be held without bail considering the charge is murder. Would he be found guilty? Maybe, maybe not. But "Delivering Mata'ke's judgement" and "she does not want to know" "She would be obliged to act." [because he's talking to security personnel] "A Vaurca tried to get rid of Easter's body. He has squashed a bug." is abundantly incriminating. Committing a murder on a canon event round where intelligence forces were present was extremely bold and high risk. And well, sometimes the risk pays off and sometimes it doesn't. You really rolled the dice on this, and if it weren't for that PDA message I would have felt you had sufficiently covered your tracks.
Here are the issues I have with the procedure for how it was handled. Resi did not consult me or get definitive and explicit approval from an administrator before moving forward with this. I've been largely spotty in my availability since Christmas since the Christmas season was very hectic for me, I was very ill for a few days, and then after that illness I lost my computer for a few days. So this may be why Resi went to Kyres about it instead of myself, since at the time I was essentially deflecting all my responsibilities to my deputy. I'm also not a fan of how it took some weeks before a decision was made and the player was informed, though this was explained by attempting to work through taj team first before discovering Yahir was not a citizen. I still would have far more preferred if the wheels on that bus turned quicker, since I feel a few weeks was too much time to have determined those circumstances. I also would have liked, despite it possibly being out of their jurisdiction, if Lancer was consulted. Since I believe past murder cases (where the murderer had evidence and was arrested later or was caught in-round) went through CCIA. I don't remember the exact event or characters, but there is a precedent that someone who canonically murdered someone else was later ICly arrested on station by biesel authorities on suspicion of that murder.
If it's up to me (I'm not sure if it is) I would uphold Yahir's arrest, though obviously he wouldn't just automatically be found guilty. I dunno how a court case would turn out, but it would take so long anyways assuming there wasn't a confession that it's functionally removing the character anyways, at least for a year, and if he confessed it would still mean removal. Does it suck? Well yes, but committing a canon murder carries exactly this risk with it. I'd really say don't kill someone on extended/during a canon event unless you're fully prepared for the possibility of losing your character. A lot of killers aren't exactly caught within moments of their crime anyhow, the fact that he wasn't discovered in round isn't entirely of consequence here. Both because we already have a precedent when the police boarded the station on extended and arrested someone for a canon murder they did in a different round and because being arrested some time later is usually what happens to murderers.
On the subject of overruling the decision to make an exception for good roleplay: I'm unwilling to do this. If a character not everyone liked was in the same situation, should they get a pass? Just because people like Yahir and because Bear's roleplay was well received doesn't mean I can say the canonical murder was fine and the police totally let him off the hook. If George Melons the greytider did the same thing but roleplayed it in such a way where it was clear he wasn't griefing and it had to be handled ICly, I would have come to the same conclusion. The stakes for canon murder have to be high to make sure its both rare and sweet to pull off (I've heard tales before of people who have pulled it off). Just like a good roleplayer may be slapped with an IR rather than the modmin team for good roleplay where they did bad things, so too do I feel this is the appropriate consequence.
If my superiors feel differently and would like to hand down a different ruling, I will defer to their judgement. However, due to my disagreements on procedure I am going to give a lore team warning to @resi based on the means utilized, even if I agree with the ends.