Tiger-bone liquor made by a zoo in northeast China's Liaoning province where 13 Siberian tigers have died in the last three months is an open secret, the Beijing News reported Wednesday, citing an unnamed source from the zoo.

Regulations require bones and skin from dead tigers to be sealed up for safekeeping, but they don’t specify which department should keep the tiger remains, so they end up being kept by the tiger keepers, said the source from the Shenyang Forest Wild Animal Zoo.

The practice of making tiger-bone liquor in the zoo started in 2005 and the liquor was mainly served to the upper-level departments, including the forestry bureau, parks and gardens bureau and the police bureau, an unidentified person in charge of the zoo told the Beijing News on March 14. "I myself have also drunk the tiger-bone liquor," the person added.

The Beijing News cited another source familiar with the matter as saying that some departments were aware that the zoo was using tiger bones to make liquor but they didn’t object to this practice. "Only sales to the public were not allowed," the source said.

Almost 50 tigers have died in the zoo since 2000, and each required a refrigerator to store the body, which cost the zoo thousands of yuan each month in electricity bills, an unnamed insider said.

Investigation into the matter is ongoing.