Sankar, 22, was hacked to death on a crowded road in broad daylight. People watched in horror as the attackers then fled on a motorcycle.
He was murdered for marrying a woman from a higher Hindu caste, police say. She was also injured in the assault.
Dalits, formerly called untouchables, are at the bottom of the caste system.
The bride's father, who handed himself in and admitted to carrying out the attack, was one of those sentenced to death.