API not returning all tweets in list


I’m trying to retrieve the most recent 3 tweets from a list set up on a user account. However, not all tweets are being returned and I can’t figure out why.

The list is here: https://twitter.com/CranfieldBR/cranfield-users
and the API request is: https://api.twitter.com/1/lists/statuses.json?slug=cranfield-users&owner_screen_name=cranfieldBR&per_page=3&page=1

Any ideas?