The tiger, named Cracker, died after eating food laced with carbofuran in April last year, it has been revealed.

Carbofuran is a highly toxic pesticide.

The poisoning came to light after a private organisation called on the Thai prime minister Prayut Chan-o-cha to examine the poisoning of the highly endangered Siberian - or Amur - tiger at Ubon Ratchathani zoo.

Only some 600 tigers exist in the wild in the Far East of Russia.

The man who exposed the scandal - Srisuwan Chanya, chairman of the Stop Global Warming Association - said: ‘The zoo and Zoological Park organisation did not release any news on this.

‘On the contrary, they tried to cover it up.’

There was a delay of six days ins ending samples of the dead tiger for a biopsy - and it was later found by police that zoo workers were implicated by police in the poisoning and sale of the skin.

‘Its death was significant because the breed is an endangered species under the 2008 IUCN [International Union for Conservation of Nature] Red List of Threatened Species,’ said Mr Srisuwan.

‘However, the chiefs of the two organisations have failed to take action or investigate the death.’

Tiger skin, carcass and organs are in demand for decoration purposes and unproven aphrodisiac properties, he said.

Yet this tiger was bought with taxpayers’ money in Thailand.

There had been no proper investigation, with punishments for tax oversight, he said.

Police identified the suspects as Prawit Thongbai, 27, and Vichai Taethaisong, 39, the tiger's keepers who allegedly mixed Furadan, the commercial name of the carbofuran substance, in its food.

The pair allegedly asked Surachai Kwamsawat, 37, a former worker at the zoo, to steal the skin on 26 April to be sold to Amnat Inchukul, 29, a Bangkok trader for 20,000 Baht.

The two keepers were charged but denied poisoning Cracker.

The alleged accomplices were also charged last May with criminal offences.

The court is still ‘reviewing’ the case, according to reports.