Expressing suspicion over the cause of death of their son, whose body was found along railway track in Dharmapuri, Ilavarasan's parents-- T Elango and Krishnaveni, accompanied by their advocates, told reporters here that police had not investigated the various angles in the case.
They alleged that selective leaks to media were being made to show that the death was a suicide.
Elango alleged that they were lapses in the police investigation as they did not span out to nearby areas for clues and did not deploy sniffer dogs.
Ilavarasan's marriage with an upper caste girl Divya in October last year triggered caste clashes in parts of Dharmapuri and the girl later chose to live with her mother as her father committed suicide over her tying the knot with a dalit boy.
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A day after Divya said she would not return to her husband, Ilavarasan's body was spotted on a railway track on July four.
The first post mortem was conducted without family consent, which forced him to move the High Court, leading the court to order a second autopsy by a team of doctors from the All India Institute of Medical Sciences (AIIMS).
Elango and senior advocates NGR Prasad, R Sankara Subbu and Rajnikanth said that police should probe certain claims that locals had heard some men arguing in the area where Ilavarasan was found dead.
"It is clear that the police has not carried out the investigation in the right manner. Also, there is no action on a petition seeking transfer of a DSP investigating the incident. Therefore we seek transfer of the probe to CBI or a Special Investigation Team (SIT) for impartial investigation," they said.