For my blog, I recently read through the first 20 months of Superman stories in the comic books and the comic strips and I could not find a single case where I could say beyond the shadow of a doubt that Superman killed anyone by his own direct action and with intention. For sure, there are many scenes where you could guess that this henchman or that one probably bought the farm. But it's never shown on panel.
There's one daily where Superman throws a couple of sailors in the sea--a sure recipe for death as I know from my experience in the navy. But the ship those men were on gets blown up seconds later and only Superman manages to survive, just barely. So either way--if they hadn't been thrown in the sea or their shipmates had recovered them from the sea--those seamen would be dead anyhow. In fact, for all we know, Superman might have saved them, because maybe Aquaman came along and took those guys to safety and they were never caught in the blast from their ship.
I'm just saying, if you want to, there's always an out you can find for any deaths that Superman might have caused in those early adventures. Yet these are the ones where so many say that Superman was his most violent and most killing. Perhaps I have to read further ahead.
I know there was that time in the Byrne run when Superman killed the Phantom Zone criminals. What else?