Construction magnate Premchai Karnasuta has denied poaching charges levelled against him and three others.
They were arrested earlier this month in the sanctuary in western Thailand where rangers stumbled on their camp and found guns and animal carcasses.
Rich and influential Thais have a habit of avoiding justice.
The junta which seized power in 2014 is on the back foot over a luxury watch scandal that has engulfed the defence minister, and allegations that the ex-police chief borrowed nearly $10 million from a fugitive brothel owner.
Chaiwat Limlikitaksorn, head of a special task force with the Department of National Parks, Wildlife and Plant Conservation, said the discovery of the excrement was important because it was near the campsite and he did not believe Premchai would wander deep into the woods for such a purpose.
He said the excrement was suspiciously close to spent bullet casings and the location where the panther was skinned.
“It can prove that he was there, he cannot say he was not there,” Chaiwat said, adding that the waste would be tested for Premchai’s DNA.
Premchai, president of Italian-Thai Development Company which built Bangkok’s Suvarnabhumi airport among many other major projects, denied poaching after his arrest.
He and his camping colleagues have been bailed while the case is under investigation.
The Thungyai Naresuan national park where Premchai was arrested is in tourist-friendly Kanchanaburi province.
The slain animals at the campsite were a black leopard, a Kalij pheasant and a red muntjac or barking deer — protected species under Thai conservation law.
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