You must have been the owner when the taxes were assessed. Then, any property taxes you pay are deductible as of the date paid, regardless of what year they were incurred. However, there is still a $10,000 cap on all state and local taxes as itemized deductions.
If you bought the property and must pay back taxes to clear the title, that is treated for tax purposes as an increase in the purchase price, and may reduce your capital gains in the future, but is not deductible.
