Case 1: Petr shoots and kills Anna while hiking, thinking that Anna is a dangerous bear (she was wearing a fur coat).
Case 2: Ivan the NKVD agent shoots and kills Natasha for speaking out against the state, thinking it is right to kill dissidents.
Both Petr and Ivan acted in ignorance. If their ignorance was inculpable, then they might well be inculpable for their respective killings. However, even if neither is culpable, it seems that Ivan is now a murderer while Petr is an accidental killer.
Wherein lies the difference? Both killed someone who shouldn't have been killed. Both did something that would have been a case of culpable murder if they killed while knowing all the relevant facts.
One difference is this. Petr acts under this description: "Killing something that appears to be a dangerous bear" or maybe even: "Killing a dangerous bear." Ivan acts under this description: "Killing someone who spoke out against the state." The description that Petr acts on is a description that it is permissible to act on (regardless of the version we choose). The description that Ivan acts on is a description that it is always impermissible to act on. Both Petr and Ivan have deficient knowledge. But Petr's intention is acceptable while Ivan's is corrupt.
I am somewhat inclined to go even further. Of the two, Petr did nothing morally wrong. Ivan, however, acted wrongly, albeit perhaps inculpably. This works best if we take Petr's intention to be "Kill a dangerous bear." In that case, we can say that Petr's action was a permissible attempt to kill a dangerous bear. But Petr's action was unsuccessful. On the other hand, it seems that Ivan's intention to kill a dissident made his action impermissible but successful.
Maybe. But what if Ivan's intention was this: "Permissibly kill Natasha for being a dissident"? In that case, Ivan failed, too, since his killing wasn't permissible. But now it seems we have a close parallel between Petr and Ivan. Petr failed to fulfill his intention to kill a dangerous bear. Ivan failed to fulfill his intention to permissibly kill Natasha. Can't we, in fact, say that just Petr accidentally killed a human, Ivan accidentally killed someone that it was impermissible to kill? So can we really say that Ivan was a murderer but Petr wasn't?
I don't know. There is, nonetheless, this difference. The intention "Kill a dangerous bear" is one that it is possible to succeed at. The intention "Permissibly kill Natasha for being a dissident" is one that it is not possible to succeed at. (Admittedly, there may be cases where it's permissible to kill a dissident. But even in those cases, it's not permissible to kill the dissident for being a dissident. Rather, the cases of permissibility are ones where there is some reason for the killing over and beyond the dissident's dissidence.) But while this is a significant difference, it doesn't seem to be a morally significant difference. After all, just as "Permissibly kill Natasha for being a dissident" is impossible to succeed at, so too "Find a counterexample to Fermat's Last Theorem" is impossible to succeed at. However, there is nothing morally wrong with someone who tries to find a counterexample to Fermat's Last Theorem in ignorance of the impossibility.