A man entered the Little Collins Street shop on December 30 last year about 4.30pm.
He picked several pieces of jewellery and paid for the items with a credit card.
It was later reported to police the card used to purchase the jewellery was fraudulent, and police are now hoping to identify the man involved.
He is believed to be aged in his early 20s, with short curly dark hair and a medium build.
Detectives have released an image and CCTV of a man they believe will be able to assist with the investigation.