You need to look at the total homicide rates from before and after gun control was put in place. It does not matter to the person murdered if their murderer uses a gun or a petrol bomb. If you look at comparable populations in countries where guns are common, the murder rates are about the same. Murder is a cultural phenomena, which has little to do with the weapons used.
As an example, people of Japanese descent (when we kept such figures) in the United States, where guns are plentiful and easily available, had murder rates slightly lower than Japanese in Japan.
You are here separating out homicide as unrelated to any other type of crime, whereas it seems to me to be on a continuum with other types of violent crime, since it seems unlikely to me that violent criminals balk at murder when they are perfectly willing to commit other violent crimes.
IOW, those societies which have more violence in general will also have higher homicide rates, all other things being equal. Yet most European countries have a violent crime rate that is a multiple of that in the USA, but a much lower murder rate. The most logical (partial) explanation of this odd fact, to me, is that violent crimes in these countries are committed using less-efficient weapons, thus fewer result in deaths. As somebody has pointed out, it’s really difficult to do a drive-by with a knife.
As far as comparing homicide rates before and after gun control is put in place, I don’t know of any country with a high homicide rate and widely available guns that later put in place effective strict gun control. So I don’t know of any case where this experiment was done. If you know of one, I’d love to see it.