Pak Kret police in Nonthaburi north of Bangkok were called to the 13th oor of a 14 story condo on Thursday afternoon after a 60-year-old American man was found dead in his room.
Named only as Donald he was discovered by a security guard who noticed a smell coming from his room.
A spare key was located. Doctors estimated the man had been dead for between 2 and 3 days.
They determined there were no outward injuries on the body that was taken away for autopsy at Thammasat Chalerm Prakiat Hospital.
A note apparently written by the deceased spoke of pain and personal troubles and mentioned that he loved Thailand, reported Sanook.
Several bottles of prescription medication were taken into evidence.
No cause of death has yet been ascertained.
The victim rented the room and lived alone and was last seen on June 21st.