Authorities say Onthank left the siamang at the Lionshare Zoological Center in Greenwich and Stamford in October while trying to sell his house.
The Connecticut Department of Environmental Protection says he never had a permit for the animal, as required by a 2004 state law.
The charge comes a month after a Stamford woman was mauled by a pet chimpanzee. That incident prompted the state and Congress to consider strengthening laws about exotic pets.
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