A bitter legal wrangle unfolded after 50-year-old teacher Preecha Kraikruan filed a complaint that he had lost the five lottery tickets which won a draw last month.
Authorities discovered the 30 million baht ($920,000) prize had already been collected by retired policemen Charoon Wimon, 62, in western Kanchanaburi province.
With both parties claiming the cash is rightfully theirs, forensic police are now stepping in to determine whose finger prints match the ticket stubs.
A forensic official with the justice department said the results are expected next month.
The government-run lottery, which is drawn twice a month, has a fanatical following in a kingdom where nearly all other forms of gambling are banned.
Many punters in the superstitious country turn to "lottery numerologists" to choose ticket numbers, often linked to special dates or other auspicious events.