(CNN) An Indian court has sentenced a former politician to life in prison for inciting anti-Sikh violence in riots after the 1984 assassination of Prime Minister Indira Gandhi which claimed thousands of lives.

Sajjan Kumar was a key leader of Gandhi's then-ruling Congress Party when she was gunned down by two of her Sikh bodyguards. They killed her four months after she ordered Indian troops to storm the Golden Temple -- one of Sikhism's holiest shrines -- to flush out separatists.

Kumar previously served as a leader of Congress, which ruled the country for most of the post-independence era but is now the main opposition.

His conviction relates to the killing of five Sikhs in West Delhi in the days after Gandhi's assassination. The court relied heavily on three eyewitnesses -- including Jagdish Kaur, who was the wife of one victim, the mother of another and cousin of the remaining three.

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