Genocide on the Infinite Express

A man with no name and no memory finds himself on board a train of infinite length, filled with corpses. All of the corpses are clones of himself, dead versions of him, and no two are exactly the same. They have different haircuts, or beards dyed wild colors; some have tattoos, or piercings, or scars, missing or multiple limbs, or weirder still, are a completely other species... there are dwarf versions of him and dinosaur versions of him and even cartoon cereal box mascot versions of him, all gruesomely murdered. Who is he, who are they, who murdered them, and why? What else can he do but walk, and hope to find answers to the ultimate murder mystery somewhere amongst the endless corpses?