One among the arrested was a college student, they said, adding a hunt was on for three others.
The death of Gokulraj, 26, had triggered protests by his family here who had gone on an indefinite fast on June 29, along with some Dalit outfits, demanding a CBI probe and that a case of murder is registered, instead of suspicious death as initially done by railway police.
They had alleged that it was an honour killing as the youth was in love with a girl of another caste.
The family gave up the indefinite fast on Thursday upon being informed of the arrests and received the body.
Gokulraj's friend had moved the Madras high court, which directed constitution of a team of doctors to perform the autopsy and for the report to be placed before it.
On June 30, the court had directed the registrar general to submit the report to the investigating officer.
The case was later changed to that of kidnap and murder by police on the direction of the high court.
DIG Vidya Kulkarni said the love affair had led to the murder.
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