Rahmat Asadi has the reputation of being a cold and calculating killer who numbers a billionaire among his victims.
Officials in Dubai have warned Thai authorities and urged them to take every measure to capture Asadi. Airports throughout Thailand - including Phuket International Airport - are on alert.
Asadi arrived in Bangkok's Suvarnabhumi International Airport on Wednesday on flight TKD068 from Dubai. He has not been traced since on any internal flights.
Police fear he could have fled Bangkok by car, bus or train and could now be holed up in Phuket, Samui or Pattaya.
Phuket shares top of the list because recent reports about the missing MH370 flight have exposed the ease with which passports can be stolen and sold on the holiday island.
More criminals are likely to believe they can reinvent their identities easily while visiting the popular international spot, posing as tourists.
Asadi could also simply try to lose himself in cosmopolitan Bangkok, as many other people on international wanted lists have done before him.