If you steal property, you must report its fair market value in your income in the year you steal it unless you return it to its rightful owner in the same year.
Lesson learned. Steal on Jan 1st 00:01, return to owner on Dec 31st 23:59, rinse repeat.
While the US government's fiscal year starts in October, and many employers have fiscal years not starting on Jan 1, individual taxes are generally calculated by the calendar year. Form 1040 defaults to that unless you write in otherwise.