Wordpress - Find out who deleted a page or post?

By default, no, WordPress doesn't keep track of who changes post statuses (at least that I can see).

you can hook into transition_post_status and log the user id.

    add_action( 'transition_post_status', 'wwm_transition_post_status', 10, 3 );

    function wwm_transition_post_status( $new_status, $old_status, $post ) {
     if ( 'trash' == $new_status ) {
      $uid = get_current_user_id();
      //somehow or another log the $uid with the $post->ID
     }
    }