The body of Shanmugavelu, who was working in the dispatch section at the Collectorate, was found hanging in the second floor of the Noon Meal (wing) section room, police said.
A collectorate official was being questioned for allegedly threatening Shanmugavelu, a Dalit, to bring some letters to the collectorate.
Shanmugavelu had reportedly told members of his family that he had to go urgently today as he had been given a deadline to complete some work.
Some supporters of Dalit leader John Pandian gathered outside the Collectorate demanding an investigation into the reasons behind his death and alleged threats against him.
Muthukumaraswamy allegedly committed suicide on February 20 by jumping in front of a train.