The animal was found dead in the national park last month. The forest authorities were mum on the cause of the death and had ruled out any foul play.

However, the viscera report received on Wednesday revealed that the big cat was killed by poisoning its kill, a large antelope.

Authorities had last month ruled out poaching citing the intact body as proof, and now claim that it was stepped up vigil that did not allow the poachers to remove body parts.

Even when they were in denial mode, the authorities had received a tip-off that two residents of Karivah village — Laxman and Rai Singh — were involved. The forest department had no proof, but took them into custody after receiving the viscera report from a laboratory in Sagar.

During investigation, poison was seized from their homes. Their interrogation led to the arrests of four more persons — Ramratan, Ajit Singh, Sukhram and Samaru.

Principal Chief Conservator of Forests (Wildlife) P B Gangopadhyay said it was yet to be established at whose instance the killing was carried out but it seems an ‘‘outsider’’ was involved. Apart from the forest authorities, the district police are also investigating the matter. Suggesting that a gang from outside the state was involved, Gangopadhyay said the case would be handed over to the CID to probe the outside link.

Gangopadhyay who rushed to the national park said the purpose (behind killing) was definitely trading but claimed that a massive surveillance was on. ‘‘It’s impossible to put an end to such surreptitious poisoning,’’ he said.

What has made the Kanha National Park authorities sit up is the seizure of the skins of a leopard and a spotted deer from the house of Biran Chander Singh Gondh from Narna village. A tip-off led the forest authorities to Gond’s house from where they recovered poaching equipment. The leopard’s bones and flesh were also recovered from the house. It was not clear when the leopard was killed.