A Sumatran tiger and two African lions have died at a zoo in Indonesia after eating rat poison.
The animals died at the Taman Rimbo Zoo in Jambi after zookeepers noticed that their health was failing.
The lions, Gebo and Sonia, and the tiger, named Peter, were struck with sudden paralysis and died five days later, the Jakarta Globe reports.
Nurzaman, the head of the Jambi Natural Resources Conservation Agency, said laboratory tests showed the animals died from strychnine poisoning, a toxic substance often used as rodent poison.
"The poison is commonly used to kill stray dogs that may spread rabies. This type of poison is not sold freely. So it is a clue as to who may have killed the animals."
A tiger cub named Ayu also suffered from poison symptoms but is now recovering.
Nurzaman said four people had been questioned as part of a police investigation into their deaths, but did not name any suspects or potential motives.
Taman Rimbo Adrianis, the head of the zoo, said the two lions had come from a safari park in West Java and had only arrived last month.
According to Indonesian news website Viva News, Nurzaman said two of the people being questioned were meat suppliers for the animals in the zoo. A nurse and a night watchman were also being interviewed.
"The lions were the visitors' favourites," he added. "Since the pair of lions arrived, the zoo revenues had increased compared to last year."
Sepdinal, the head of Animal Husbandry and Animal Health for the Jambi Province, also noted that the poison is only sold through certain distributors and told reporters how the poison works: "Dogs die a few hours after eating strychnine. Toxins damage their organs and nerves, and damage the heart muscle, resulting in death."