AG Perarivalan was in jail for over 30 years. In 1998, he was sentenced to death, but it was later commuted.
Arrested at 19, Perarivalan was convicted for procuring batteries that were used in the bomb to kill Gandhi.
Gandhi was assassinated by a female suicide bomber as he addressed an election rally in Tamil Nadu state.
Gandhi's killing was widely seen as retaliation for his having sent Indian peacekeepers to Sri Lanka in 1987 when he was prime minister.
Perarivalan was a member of the Liberation Tigers of Tamil Eelam (LTTE), a rebel group fighting for a separate Tamil state in Sri Lanka. The rebels were finally defeated by Sri Lankan troops in 2009.