CORRECT: Back then, you (or one) could be killed for any trifle.
There was very dangerous at that times because you would be looted, taken a beating and even gone home in a box...
It was very dangerous in those times; you could be robbed, beaten, or even sent home in a box.
"could have been killed" would mean that, at some point in the past, a situation arose where the danger was great enough to result in death, but death did not occur.
Why did you jaywalk across the busy street at rush hour? You could have been killed!
Twenty years ago, there was no pedestrian crossing or traffic signal at this busy location. You could be killed trying to cross the street.