Adam GrettonThe mystery behind the death of an internationally important Siberian tiger may never be solved, a Norfolk zoo director said yesterday .Adam Gretton

The mystery behind the death of an internationally important Siberian tiger may never be solved, a Norfolk zoo director said yesterday .

Further veterinary tests are being carried out on the body of five-year-old Malyshka after she was found dead in her enclosure at Banham Zoo on April 18.

But zoo director Martin Goymour yesterday said investigations into the death of the pregnant tigress may prove to be inconclusive.

A post mortem examination found that the Siberian tiger had drowned in the shallow pool of her enclosure, but not received any significant internal or external injuries.

Mr Goymour added that the involvement of Malyshka's mate Mischa had been ruled out, as had any defect with the enclosure or the pool.

'The senior independent veterinary officer is awaiting further results from the laboratories from pathology samples previously sent, however his opinion is that they may well be inconclusive. Such conclusion would direct further enquiries towards the possibility of a brain seizure or fit,' he said.

He added that further tests of Malyshka's brain had been authorised.

'Mischa, with the two 17-month-old youngsters Vasya and Kuzma, continue to occupy their two and a half acre enclosure and have access to all facilities. Regular zoo visitors have been very supportive in their comments and in support of the zoo and the animal keeping staff,' he said.

There are only 400 to 500 Siberian tigers left in the wild, with an additional 500 in zoos worldwide. Malyshka had been one of the most important females in the European breeding programme.