Did Kurosaki Ichigo actually kill someone

Why wasn't a single Shinigami surprised that Ichigo had Zanpacto?

Ichigo may seem like an outlier, but in fact there was another character mentioned by Nimaiya himself who wasn't a Gotei member but had a Zanpaktou, Zaraki. Kenpachi Zaraki took an asuchi from a dead Shinigami that he may or may not have killed first. This gave him a Zankakuto with which he had great success against the then Kenpachi. This shows that Asuchi are transferable to a certain extent.

Second, and also importantly, when Ichigo first got his powers, he got them from Rukia. Rukia was an above average Shinigami who already had Shikai. When she gave him his powers, she didn't find it strange that he had a zanpakuto, rather she found that his massive size was strange. She, someone who had to get an asuchi in order to have a zanpakuto, didn't focus on Ichigo's possession of one, which suggests that she gave him hers.

So, Ichigo most likely got his asuchi from Rukia, but that leaves a couple of plot holes in place. When did she get it back or did she ever do it? If she never got it back, why did Nimaiya say he didn't have one, and why did Rukia clearly have one during the arancar arc?

It all boils down to being a plot hole. Asuchi weren't fully elaborated at the beginning of the series so they remained largely vague. But that is not the question here. The question is, why weren't they surprised he had one? The best answer for that is unfortunately just the theory, the theory that they thought he still had Rukias Asuchi or maybe someone else's. As mentioned on Zaraki, it is entirely possible for non-Gotei-13 members to get Asuchi, although this is rare. In any case, they didn't care. If they had thought about it, they would probably have thought that he stole / borrowed it from Rukia, or maybe even though an unknown agent received a second one.

When he showed up he basically had a zanpakuto how he got it was irrelevant to her. Although very rare, there have been other methods of getting an asuchi other than becoming a Gotei 13 Shinigami. From a plot perspective, it's a hole. One can only theorize how it all happened. My personal theory on this is that Byakuya broke it, and since he lost Rukia's powers at that time, it never healed and was discarded. Rukia then probably got a new one from Gotei 13.

絢 瀬 絵 里

Or they suspect that other refugees like Urahara Keisuke and Shihouin Yoruichi brought one for him. If you know Urahara's genius, you won't be surprised that Ichigo has a zanpakto.

Ryan

@ AyaseEri Very true, maybe I should have said more than a simple sentence about the possibility of someone else giving them one as this is basically one of the few other ways. I think a shinigami has to be involved somehow in order to get one, which amounts to being gifted or stolen.