Explain in 1-3 paragraphs what Meursault means when he says, “It was back to my cell...sleep of the innocent.” Explain why he describes himself as “innocent.”

I think that Meursault is embracing his existential chaos here. Meursault does not think of prison as the logical consequence of crime but rather an extension of the absurdity of life: it is a totally arbitrary fate and prison is just another chance of fate- as valid as visiting the beach. This absolves Meursault of any vestiges of guilt he might have of killing the Arab: he can now enjoy "the sleep of the innocent."