The 26-year-old motor mechanic was chased by a policeman after he pelted stones at passing trains in the seafront Bambalapitiya area of Colombo on Thursday, Oct 29.
According to police spokesman Nimal Mediwaka, "The victim had been beaten and prevented from reaching the shore, resulting in his drowning. The constable has been arrested."
TV viewers watched with horror on Friday night, Oct 30, footage of the man being chased by the policeman and another unidentified man who beat him with sticks until he collapsed in the water and drowned.
The relatives of the man said that the mechanic had been receiving treatment for a mental disorder.