A Royal Bengal Tiger cub died under mysterious circumstances at Itanagar zoo in Arunachal Pradesh last night, a day after four tigers in the zoo fell ill following suspected food poisoning.Sources said it has been suspected that miscreants mixed poison in the food provided to the animals on Sunday evening, which resulted in four of the big cats falling ill. The vets put in their best efforts with locally available resources, to which only three of the tigers responded positively. But one of them died. The dead tiger is said to be about two years old and was born in captivity in the Arunachal capital itself. Although no arrest has been made so far, 15 employees of the zoo were picked up for interrogation. A departmental inquiry has been ordered into the matter.