dropdown select in cakePHP


I am using CakePHP 1.2. I have a person model that hasMany 'Document'. When I edit a document, the select box for the owning person appears (echo $form->input('person') where person has been defined in the documents_controller like this:

$allPeople = $this->Document->Person->find('list', array('fields' => array('first_name')));
$this->set('people', $allPeople);

When I edit a document's record, I want the person owning the document to be selected and displayed in the box. Right now, the app just makes the list box but doesn't highlight the correct owner (though the DB has the person's id).

Thank you,
Frank Luke