we remember everything that happened in oshwittz and the other concentration camps as well as the kate in other places during terrible five or six years that such events never 
We should remember everything that happened in Auschwitz and the other concentration camps, as well as the murders committed in Katyń and other places during those terrible five or six years, so that such events are never repeated.
We remember everything that happened in Auschwitz and the other concentration camps, as well as the Katyń other places during terrible five or six years, that such events never repeated.