The 21-year-old victim seemed to slip and fall on to the tracks as the train pulled into a station in the capital's Sodermalm district early Sunday.
"The air pressure from the approaching train could have contributed to him losing his balance," police spokesman Jonas Palm told the Swedish news agency TT.
Alcohol was also suspected as a contributing cause, TT said, and the man's friends did not believe he committed suicide. The incident was being investigated as an accident.
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