The police on Monday released camera footage showing Mac Thanh Thao's husband dropping the watch at the security screening area when the family was leaving Phu Quoc for Ho Chi Minh City after a three-day trip to the island on December 25 last year.
A female passenger later picked up the watch without reporting to the airport officials, the police's footage showed.
The woman returned the watch early this month and the police gave it to Thao's relatives two weeks later, police said.
Thao, 35, and her family members had put their personal belongings including the watch in a bag and placed it in a tray at the security check area.
At the other end, she found her watch missing. She immediately complained to customs officers.
Within a few days airport officials sent four video clips and three related photos to the police for further investigation.