Question
Did G-d Himself kill the Egyptian first born?
Answer
As we read in the Hagadah, Ex. 12:12 clearly implies that G-d Himself would smite the Egyptian firstborn; the verse uses the first person three times, and ends with "ani ha-Shem". But in 12:23, when Moshe tells the Jews what will happen, he implies that ha-Shem would be accompanied by a "mashchis" who would do the actual killing. (This is not the only place in the Torah where Moshe "softens" G-d's words when he conveys them to the people.) From the wording of 12:23 it seems that the mashchis operated in the Jewish houses that didn't have blood on their doorposts.