The Supreme Court described the attack as "barbaric and heinous and a crime against society." It also condemned the police for not helping the students on board the bus.
"At the time of the incident, police media were present at the place of incident. None of them came for help. The police should not have been silent. Why the police didn't help?" asked the court.
In 2000, more than 40 students and two teachers were in a bus that was attacked by AIADMK members to protest against the conviction of their chief, Jayalalithaa, in a criminal case.
The death sentence had first been given by a trial court in Salem and was then upheld by the Madras High Court in 2007.