Scientific analysis also establishes the handwriting on the suicide note is Ilavarasan's, say the police.
Investigators claim Ilavarasan had called his close friend, informing him of his death mission, from the location of his death. He was also drunk at the time of his death they add.
The Kurla Express that's believed to have hit him had blood traces, but no scientific matching has been done yet.
Refusing to accept the police theory, Ilavarasan's parents suspect their son was murdered and body thrown near the track. Even the handwriting on the suicide note, they claim, is not their son's.
They ask how the body was intact if a train ran over him. Two, why was the liquor bottle, found at the site, sealed? They also wonder why it took four days for the police to find the suicide note.
The first post-mortem report, rejected by the High Court, said he died of head injury. The second autopsy, performed by a team of doctors from the All India Institute of Medical Sciences, submitted its report to the court on Monday.
Ilavarasan married Divya, an upper-caste Vanniyar, in October last year. Her father committed suicide following around 250 Dalit homes were set on fire allegedly by Vanniyars backed by the Patalli Makkal Katchi (PMK). The party has denied the allegations.
A fortnight ago, Divya said she would not return to her husband. Ilavarasan was found dead the next day.
Was it a murder or suicide? The truth may take a long time, but for Dalits in Tamil Nadu, Ilavarasan's death is a rallying point and he's already a martyr.