A bag with 6,000 methamphetamine pills and a homemade gun was found abandoned at the Lak Si railway station in Bangkok on Wednesday.
Thung Song Hong police were alerted at 8.30pm to check a black travelling bag which had been left left at the station.
Police found a homemade .38 revolver and 6,000 meth pills in the bag.
Security camera footage at the railway station showed a lean man, who appeared about 170 centimetres tall, carrying the bag at 5.20pm on Monday.
When patrol police from the Thung Song Hong dropped by to check the station, the man got up and walked out of the station and did not return.
Security officials at the station called police as the bag had been left unattended for days.