Palash Karmakar, an attendant at the State Biological Park in Itanagar, was killed by a tiger when he entered its enclosure for cleaning on Tuesday afternoon.
Preliminary investigation indicated that the door of the Royal Bengal tiger's cage was not closed after feeding allowing it to come out and pounce upon the 35-year-old Karmakar, killing him instantly.
He had gone inside to clean the water body.
A case of unnatural death has been registered at Itanagar police station.
