Investigation was on to nab the culprits, he said adding the forest department was also initiating a separate departmental inquiry into the matter.
Itanagar Zoo, 8 km from the town and established in 1987, is spread over 250 hectares and its display area is approximately 41 hectares.
Along with six big cats, the zoo also housed nearly 200 animal species.
On February 21, 2006, three tigers and a leopard were poisoned inside the zoo by miscreants. One tiger had died, while the other two along with the leopard had survived, zoo authorities said.