No one but him could have told them that the theif was I.

a. him could have told them that the theif was I.
b. he could have told them that the theif was I.
c. he could have told them that the theif was me.
d. him could have told them that the theif was me.
e. he could have told them the theif was me.

The OA is A. Can someone explain why?