Chennai, Jan 13 (Reuters): Kausalya and her husband of eight months were shown no mercy when they were attacked by a group of men armed with knives and sickles in a crowded market in the Udumalpet town in Tamil Nadu last year for daring to marry out of caste.

Kausalya, now 20, was left bloodied and dazed by the attack captured on security cameras and viewed throughout India but her husband, Sankar, 22, died from his injuries, inflicted as he was a low-caste Dalit and had married a woman from a higher caste.

A couple of weeks ago, in front of television cameras, Kausalya voiced her relief that her testimony had helped bring death sentences against her father and five others who killed Sankar.

It was only the second instance of capital punishment awarded by a lower court in India for caste-based honour killings, which have risen sharply in Tamil Nadu over the past decade even as convictions remain rare, activists say.

"I gave testimony against my family because I don't see them as family, but as criminals who had to be brought to justice," said Kausalya, who is from the powerful Thevar community. "I don't want another Kausalya and Sankar to suffer the way we did," she said.

The case of Kausalya, who asked the court to reject the bail petitions of the accused 58 times, is particularly significant, as she was a witness who became a crusader, said Kathir, founder of Dalit Charity Evidence, which helped her through the trial. Kausalya now intends to appeal the three acquittals in the case, including that of her mother.

"These cases are usually not even registered by the police as caste-based crimes, and very few come to court. No one is willing to give evidence, least of all the Dalits, who fear for their lives," said Kathir, who goes by one name.

"This case was all because of Kausalya, who bravely took on her family. She fought for justice and became an activist against honour killings," he said.

About 500 people - mostly women - have died in so-called "honour killings" in India since 2014, according to government data, often carried out by family members who believe the relationship has brought "shame" on their community.

But activists say the crime is vastly under-reported, and that many killings are covered up to look like suicide. India banned caste-based discrimination in 1955, but centuries-old biases persist, and lower-caste groups, including Dalits, are among the most marginalised communities.

The intermingling of different castes or religions, particularly in marriage, remains taboo not only among rural populations, but even among well-off urban families.

While such killings are more common in feudalistic northern Indian states, evidence has recorded about 187 caste-based killings in Tamil Nadu in the past five years, most involving a higher-caste woman married to a Dalit man.

Such killings have surged in Tamil Nadu as women and lower-caste Dalit youths become better educated and are emboldened to oppose their families and higher-caste Hindus respectively, said V Geetha, a women's rights activist in Chennai.

"Some dominant castes have been emasculated by agrarian crises, and by the polity, and are experiencing a sense of loss and bewilderment. Meanwhile, women and Dalits are getting educated, becoming more mobile, and are pushing back," she said.

"For the higher castes, their sense of self is so tied to caste, they feel they have to preserve it at any cost. That's why we are seeing more caste violence, so much anger and aggression at these perceived threats to their identity," she added.

The first death sentence by a lower court for honour killings was handed down last year in Tirunelveli town in Tamil Nadu.

But such convictions are rare, said Kathir, who helps victims file charge sheets, get evidence and convince witnesses to testify. He wants a separate law for these killings.

A court in Chennai, last year called for specialist police units to protect inter-caste couples, and state police launched a hotline to help prevent honour killings.

But Tamil Nadu does not plan to bring a separate law, said V Amuthavalli, director of the state commission for women, citing official data that showed only one honour killing in the state last year. Kathir says there were at least 75.

"Our existing laws are powerful enough. The verdict in the Kausalya case shows the system works and the state takes stern action, so a separate law is not needed," Amuthavalli said.

Kausalya, who now lives with Sankar's family, has since cut her long hair short, and set up a tutoring facility for Dalit youths. She speaks publicly against honour killings and atrocities against Dalits. "Each day that we were married, we lived in fear. But we had dreams of a long life together," she said. "Sometimes I wish I had also died, but if I had, Sankar would not have got justice, my family would not have been punished. So many people have helped me, it has inspired me to carry on the fight against caste and honour killings."