Maybe I had better shoot him, before he shoots me, especially since, even if he doesn't want to kill me, he's probably worrying right now that I might kill him before he kills me." And so on.
"Talvez seja melhor disparar sobre ele antes que ele dispare sobre mim, "até porque, mesmo que ele não me queira matar, "deve estar preocupado  com a possibilidade de eu o matar "antes que ele me mate."