What type of unintentional killing is called wicked?

(21,13) “But if he did not premeditate it, and G-d arranged it to happen through him, I will make a place for you to which he shall flee.”

There are two types of non-premeditated killing. One is where he should have taken a precaution, for example, if one was chopping wood and a splinter of the wood flew off and killed a person, he could have guarded against this by making sure no one was standing there. The second type is where he could not have taken a precaution, for example, he was climbing a ladder and the one of the rungs broke from under him, causing him to fall on a person and kill him.

Both these types are mentioned in our posuk. When it says “but if he did not premeditate it” it is referring to an unintentional killing that he could have guarded against, and “G-d arranged it to happen through him”, refers to an unintentional killing that he could not have guarded against.

And the reason that Hashem arranged this, is “as the proverb of the ancient one says: From the wicked shall go forth wickedness” (Shmuel I - 24,7). That because “he did not premeditate it”, but he also did not guard against the killing, he is called wicked, and since there were no witnesses to the event he did not go into exile. Therefore, “G-d arranged it to happen through him”, that he will fall from a ladder and kill unintentionally a wicked person who had previously killed intentionally but without witnesses, as the gemara in Makkos 10b explains.