Innocent or Guilty?

I believe that Steve is guilty because in the beginning of the book he was trying to convince himself he was innocent. Why would an innocent person do that? I believe that he didn't mean for Mr. Nesbitt to die but if he didn't give the signal he wouldn't have died. Also if he was innocent why would he be trying to clear his mind? I mean if you're innocent you don't need to convince yourself that you're innocent. To me it's just common sense. That's why I believe that he is guilty.