Or HaChaim on Exodus 21:13/אור החיים על שמות כ״א:י״ג

1 ואשר לא צדה והאלוקים אנה לידו, If a man did not lie in wait but G'd caused it to happen to him, etc. Why did the Torah say the same thing in different words, i.e. "he did not plan it," and: "G'd caused it to happen?" Besides, why would G'd deliberately cause a person to become an involuntary murderer? Makkot 10 as well as the Mechilta dealing with the laws of the city of refuge and who has to go there, explain that the Torah speaks about wicked people who will become the instrument of performing evil deeds (compare Samuel I 24,14). They illustrate their meaning by the following example. Two people, one an intentional murderer, the other an unintentional killer, meet. There had not been any witnesses to either killing. The unintentional killer was in the process of descending from a ladder; he fell and hit the murderer who sat under the ladder with fatal consequences. The person descending the ladder has to go to a city of refuge. (If the same accident occurred while the unintentional killer was ascending the ladder, he would not have to go to the city of refuge). The intentional sinner was killed by the unintentional sinner. Thus far the Mechilta. This does not seem very satisfactory. True, the intentional murderer winds up getting his just deserts, the unintentional killer, however, has by now committed two killings and has to atone for only one killing while he is in the city of refuge. If we were to argue that he is altogether innocent concerning the instance when G'd made him fall off the ladder, then we must assume that the falling off the ladder was not an act of G'd and as a result the death of the person under the ladder was not the punishment due him as he was not guilty. Had he really been guilty then the fall off the ladder would have to be considered under the heading of "a deliberate act of G'd." This seems a very forced explanation as the Torah describes the example of an unintentional killing as unrelated to Divine interference (Numbers 35,15). The Torah did not distinguish between different categories of such unintentional killings as did the Mechilta.

2The correct explanation is that the person who was originally killed by the unintentional killer had been a deliberate murderer also. G'd could have caused some weight to fall upon such a murderer without involving the unintentional killer at all. He used the unintentional killer as His tool in order to "kill two birds with one stone." The unintentional killer who has now become G'd's tool i.e. ואנה לידו, is guilty of exile in the city of refuge only for the first time he killed unintentionally. Even if he had killed ten people as a result of his fall from the ladder, he would only be liable for exile for the original killing. The penalty of exile is related to the cause, not to the number of killings committed by the person. G'd will not arrange for this unintentional killer to become involved in a second killing in order to be exiled again. As a result of this consideration you will observe that not all unintentional killers are measured by the same yardstick. [This is nothing new since all the killers in the city of refuge go free at the same time, at the time the High Priest dies, regardless of when the people exiled there committed the killing. Ed.] We now understand the Talmud who attributed the fall off the ladder to a previous undetected and unintentional killing by the person suffering the fall. The sages simply selected an example in which both parties were equally guilt-ridden. The true scholar will understand the mystical aspect behind all this.

3It is also possible that the Torah felt that the person who was guilty of involuntary manslaughter and should have volunteered for exile in the city of refuge but had neglected to do so is now being punished for this by becoming the cause of another death. As a result he ought to spend two periods of exile in such a city of refuge. In order to enable him to expiate his guilt the Torah legislated that his stay in the city of refuge is limited; once the High Priest dies, his first exile has been completed. G'd reserves the right to determine when the High Priest should die and thereby to determine how many years such a person guilty of two unintentional killings must spend in exile altogether. While this explanation covers the words: "if G'd made it happen, etc," it still does not explain the conjunctive letter ו before the word אלוקים.

4I believe the Torah was being very specific in legislating the rules pertaining to exile in the city of refuge as related by Maimonides chapter 6 of Hilchot Rotzeach. He states that the only person who has to go to the city of refuge is one who has committed involuntary manslaughter which resulted from lack of precautions plus public knowledge that the killer did not harbour malevolent thoughts against the victim. If, however, a fatal accident could not have been foreseen and the killer had no reason to hate the victim, it is an accident and the killer does not have to go to the city of refuge. These two aspects are covered by 1) והאלוקים אנה לידו, "it was an act of G'd," or 2) אשר לא צדה, "he did not ambush the victim," (but also took no precautions to preclude an accident). If the killer had either entertained hateful thoughts against the victim or had taken precautions against any accidents there is no case for exile. In the latter case the killer is totally exonerated, in the former case there is an assumption of evil intent and taking refuge in a city of refuge is not the answer.