The Department of National Parks, Wildlife and Plant Conservation (DNP) has launched a probe to determine if five plots of land owned by Deputy Education Minister Kanokwan Vilawan and her father encroach on Khao Yai National Park.
Land title deeds for three plots were issued in 1993, while the deeds to the remaining two were issued in 2002.
Ms Kanokwan is listed as the owner of one of the plots certified in 1993, while the rest belong to her father, former deputy public health minister Sunthorn Vilawan.
According to the director of Protected Areas Regional Office 1 in Prachin Buri, Witthaya Hongwiangchan, the dates on the land title deeds are suspicious because Khao Yai was designated a national park in 1962.
"It was impossible to lawfully issue these land title deeds in 1993 or 2002 because the area was declared a national park long before that," he said.
According to Mr Witthaya, the DNP is now looking into how the land title deeds in question were acquired and/or issued and by whom.
"At this point, an initial investigation points to collusion between politicians and state officials to acquire land title deeds," he said.
Mr Witthaya said that in some cases, land title deeds were "signed by officials who had died many years ago".
"Dishonest officials received an estimated 10% kickback from land sales in exchange for their help to make the impossible possible," he said.
On Saturday, Ms Kanokwan said she was not concerned about the allegation and maintained that she legally obtained the title deeds.
The alleged encroachment came to light after the Internal Security Operations Command's (Isoc) forest protection team seized three backhoes and arrested their drivers in the national park last week.
The backhoes were knocking down trees and levelling land knolls in parts of the national park in tambon Noen Hom of Prachin Buri's Muang district. Upon seeing the team, the drivers showed officers copies of the deeds for the plots they were working on, which they claimed are owned by politicians.
Col Phongphet Ketsupha, head of the Isoc team, said yesterday his team revisited the location yesterday to collect more evidence.