Last week, Thailand's environment minister Varawut Silpa-archa ordered an investigation into the animal's disappearance, after rejecting the zoo's explanation that a python ate it.

Authorities are examining whether the rare albino barking deer -- last seen eight months ago -- was stolen.

Suriya Sangpong, director general of the Zoological Park Organisation of Thailand, was heading up the investigation and traveled from Bangkok to Songkhla Zoo for a meeting with staff on Saturday.

The 58-year-old was shot at about 11:30 am at the zoo's office, police in Songkhla said.

Officers said the gunman, Phuvadol Suwanna, a vet who also lived at the zoo, was under stress because he had been ordered to transfer to another position while the investigation was under way.

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They said he committed suicide about an hour after shooting the director.

"The gunman was (the director's) long-time friend, they were both from southern provinces," Jatuporn Buruspat, permanent secretary of the Ministry of Natural Resources and Environment, told AFP.

The organization said it would continue to investigate the deer's disappearance.

The rare animal, named Snow, was born last December and was related to a deer which was presented to Thailand's Queen Mother as a gift.

Barking deer, or muntjacs, are known for the sound they make, which acts as a warning when they encounter a threat.