Thai business tycoon and president of Italian-Thai Development Premchai Karnasuta, right, is seated after arriving at the wildlife police headquarters in Bangkok. Picture: Sakchai Lalit/AP

Bangkok - A Thai millionaire once listed among the country's richest people was found guilty on Tuesday of poaching protected animals including a black leopard at a world heritage site, a court official told dpa.

Premchai Karnasuta, president of construction giant Italian-Thai Development, was sentenced to 16 months in prison for poaching protected animals and illegal possession of carcasses of protected animals and firearms, the official said.

Soon after the verdict was read, Premchai was granted bail of 400 000 baht (12 630 dollars) and barred from overseas trips.

"I'm sorry," Premchai said to reporters before getting in a car.

Wildlife rangers arrested the 64-year-old tycoon along with four other people in Thungyai Naresuan Wildlife Sanctuary, a world heritage site in western Thailand in February 2018. 

Wildlife rangers said they heard gunshots and followed the sound, only to find the carcasses of a black leopard, a barking deer and Kalij pheasants left behind.

The black leopard - a vulnerable species - was found dissected and scalped.

The rangers, who said they were offered bribes but turned them down, also found two rifles, a double-barrelled shotgun, and various bullets by the campsite.

The incident has caused widespread public outrage, with many taking to social media to express their scepticism in the capability of the country's justice system to bring the 64-year-old to justice, saying the system often lets the rich and powerful walk free.

Graffiti depicting black leopards has also popped up in various parts of the country in a bid to pressure the authorities to find Premchai guilty.

Premchai and his sister Nijaporn Charanachitta were listed by Forbes magazine in 2016 as Thailand's 35th richest people with a net worth of 630 million dollars.